How I Build a Bear Case First: The Reverse Engineering Process That Keeps Me From Falling in Love With a Stock
The bull case writes itself. The bear case is where the real work happens.
There is a particular kind of investor mistake that has a specific texture.
It does not feel like a mistake when you are making it. The business is genuinely good. The industry is attractive. The management team has a strong track record. The valuation looks reasonable, not cheap, exactly, but defensible. You have spent three weeks on the analysis. You know the company well. You are excited about it.
And somewhere in that process, usually around week two, when the research is half done and you have seen enough to be impressed but not enough to be skeptical, you stopped being an analyst and started being an advocate.
This is the specific risk in investment research: the more you learn about a business, the easier it becomes to find reasons to own it. You read the annual reports and find the management team impressive. You study the competitive position and find the moat credible. You model the financials and find the numbers defensible. The research process, which should be a search for truth in both directions, has quietly become a prosecution of the bull case with the bear case handled as an afterthought.
The bear case, in most investment write-ups I have seen, including many of my own, is the last section. It comes after the thesis, after the financials, after the valuation. It is written when you have already decided to buy and are looking for risks to acknowledge before you hit send. Those risks, by that point, are almost always framed as manageable. They are risks you are comfortable with. How could they not be? You are already in love with the business.
I changed the order. I now build the bear case first.
Not because I am a pessimist. Not because I think most businesses I analyze are going to fail. But because the specific error I am trying to avoid, motivated reasoning, confirmation bias, falling in love with a story, is much harder to catch at the end of the research process than at the beginning. If I construct the strongest possible case for why this investment is a mistake before I start building the case for why it is a great idea, I am much more likely to see the analysis clearly rather than through the lens of the conclusion I have already reached.
Here is how I do it.
Step 1: Write the Short Thesis Before the Long One
The first thing I do when I begin analyzing a business is write down, in two or three sentences, the most compelling case for why the stock is a bad investment.
Not the risks. Not a list of things that could go wrong. The thesis. The short seller’s actual argument.
This is a meaningful distinction. Risks are things that might affect a business. A short thesis is an argument for why the market is fundamentally wrong to value the business the way it currently does, why the current price assumes a reality that will not materialize.
A risk might be: competition is increasing. A short thesis is: the pricing power this business appears to have is actually a function of conditions that are already changing, and the margin profile the market is extrapolating does not reflect where this business will be in three years.
Risks are addenda. A short thesis is a position.
Writing the short thesis first forces me to actually inhabit it, to ask not “what could go wrong?” but “if I were going to bet against this business, what would my argument be?” This requires understanding the bear case with the same seriousness a short seller would bring to it. Not as an intellectual exercise in balance, but as a genuine attempt to build the strongest possible case for the other side.
If I cannot write a credible short thesis for a business, that is not a signal to buy. It is a signal that I do not yet understand the business well enough to evaluate the risk. Every business worth analyzing has a genuine bear case. If I cannot articulate one, I have missed something.
Step 2: Identify the One or Two Assumptions the Thesis Cannot Survive
A short thesis, once written, has a structure. It depends on certain things being true. The business’s competitive position is eroding. The addressable market is smaller than the bull case assumes. The margin expansion story will not materialize because the cost structure does not allow it. The accounting is obscuring a cash flow problem that will eventually become visible.
Whatever the short thesis is, it rests on specific factual claims about the business and its future.
My second step is to identify the one or two assumptions that, if wrong, completely invalidate the bear case.
This is the mirror image of the question long investors ask about their own theses, “what has to be true for this to work?”, but applied to the short side. What has to be true for the business to be worth significantly less than the current price? And what would falsify those claims?
The reason this step matters is that it tells me where to focus the research.
If the bear case depends on the argument that the company’s apparent pricing power is illusory, that the strong gross margins are a function of a temporarily favorable competitive environment rather than a structural advantage, then the research I need to do is about the competitive dynamics of the industry: what alternatives exist for customers, whether switching costs are genuinely high, what the history of pricing looks like through prior competitive cycles.
If the bear case depends on the argument that accounting earnings overstate economic earnings, that reported profit is being flattered by choices in revenue recognition or asset capitalization that do not reflect the underlying cash generation, then the research I need to do is in the cash flow statement and the footnotes.
In both cases, I know exactly where to look, and why, before I start. The bear case has pointed me toward the empirical questions that matter most. Without it, I would be doing comprehensive but undirected research, reading everything and weighting it roughly equally, which is exactly the environment in which confirmation bias thrives.
Step 3: Stress-Test the Bull Case Against the Bear Case Assumptions
Once I have built the short thesis and identified its key assumptions, I have a framework for stress-testing the bull case.
The question is no longer: does the bull case hold? It is: does the bull case hold even if the bear case assumptions are partially correct?
This is a more useful question. It acknowledges that the bear case does not have to be entirely right to be damaging. A business that is slightly less competitively advantaged than the bull case assumes, priced at a multiple that requires the full bull case to be true, is still a poor investment even if the company never faces anything close to the worst-case scenario.
Buffett’s concept of margin of safety is relevant here, but its application is often too narrow. Most investors think of margin of safety as a discount to intrinsic value, buy at 70 cents when something is worth a dollar. But there is a prior question: is your intrinsic value estimate itself incorporating a margin of safety in its assumptions? A valuation built on the most optimistic defensible view of the business’s future is not a conservative analysis even if you apply a 20% discount to the output. The conservatism has to be in the inputs, not just in the gap between the output and the current price.
Building the bear case first ensures the inputs have been stressed. If the bear case argues that long-term revenue growth will be 6% rather than the 12% the bull case assumes, I run both. I look at what the investment looks like at 6% growth and ask whether the margin of safety is adequate given that the bear case is not implausible. If the investment only makes sense at 12% growth, if the expected return at 6% growth is inadequate, then I am making a bet on the bull case being exactly right. That is a different kind of investment than one where the returns are acceptable across a wide range of outcomes.
Step 4: Assign Honest Probabilities
After building the bear case and stress-testing the bull case against it, I do something that feels more precise than it actually is: I assign probabilities to each scenario.
I say “feels more precise than it actually is” because I do not have any special insight into the future, and probability estimates applied to business outcomes have enormous uncertainty bands around them. But the exercise is not really about precision. It is about honesty.
Specifically: it forces me to confront whether I am treating the bull case and the bear case as genuinely competing hypotheses or whether my research has effectively collapsed the probability on the bear case to something near zero.
If my honest answer is that the bull case has an 85% probability and the bear case has a 15% probability, the next question is: what is the expected return across both scenarios? If the bull case produces a 40% gain and the bear case produces a 60% loss, the expected return is (0.85 × 40%) + (0.15 × -60%) = 34% - 9% = 25%. That is an attractive expected return.
If the same probabilities apply but the bear case produces an 80% loss, because the business is more leveraged, or the competitive position more fragile, or the accounting more aggressive than the bull case assumes, the expected return is (0.85 × 40%) + (0.15 × -80%) = 34% - 12% = 22%. Still positive, but with an asymmetry that requires more scrutiny.
The calculation is not the point. The point is that it makes the bear case do actual work in the investment decision rather than being acknowledged and then set aside. A bear case I have assigned a 15% probability and an 80% loss to is a very different analytical artefact from a bear case that appears in a “risks” section and then goes unquantified. The former changes the position size and the required margin of safety. The latter is decoration.
Step 5: Identify the Early Warning Signals
The final step in building the bear case first is to define, before I buy, what evidence would confirm the bear case is playing out.
This is the most practically valuable step of all, because it determines how I monitor the position once I own it.
Every thesis, bull or bear, depends on specific empirical claims about the world. Those claims are either confirmed or denied by observable events over time: earnings reports, pricing decisions, competitor behavior, management commentary, regulatory developments. If I know in advance which specific observations would tell me the bear case is unfolding, I can monitor the position actively rather than defensively.
Without this step, monitoring a position tends to become biased in the same direction as the original research. Good news is weighted as confirmation. Bad news is reframed as temporary. Each piece of information that arrives is processed through the lens of the thesis I already hold, which is exactly the dynamic the bear case was built to interrupt.
With it, I have a specific list of things to watch for. If I see them, I update. If I do not, the thesis holds. The monitoring is structured rather than reactive.
The early warning signals should be specific, observable, and directly connected to the bear case assumptions. Not “watch for signs of competitive pressure”, too vague to be useful. But: watch for whether the next two annual reports show gross margin contraction of more than 150 basis points per year, which would be consistent with the bear case’s claim that pricing power is already eroding. If that happens, the bear case probability rises. If gross margins are stable or improving, the bear case probability falls. Either way, the position is being evaluated against the right evidence rather than against whatever happens to be in the news.
Why This Changes What You Buy, Not Just How You Think
Building the bear case first is sometimes described as a way to manage psychology, a discipline to offset optimism bias and confirmation bias. That description is accurate but incomplete.
The more significant effect, in my experience, is that it changes the set of businesses I end up owning.
When the bear case comes last, the investment analysis is implicitly structured to find reasons to buy. The research accumulates in favor of the thesis. By the time you reach the risks section, the emotional and cognitive momentum is behind the bull case. Risks get acknowledged but not truly weighted.
When the bear case comes first, a meaningful percentage of ideas do not survive it. Not because the businesses are bad, but because the short thesis turns out to be more compelling than the bull thesis, and that conclusion, reached before the research momentum has accumulated in the other direction, is easier to act on. The ideas that do survive are the ones where I have genuinely grappled with the strongest case against ownership and found it less persuasive than the case for it.
This filters toward a different kind of investment. Not the ones with the most exciting story. Not the ones that generated the most interesting research. The ones where the bull case remains more persuasive than the bear case even when the bear case has been built by someone who was trying to make it as strong as possible.
Those are the positions I trust. They are also, in my experience, the ones that tend to hold up when the inevitable period of uncertainty arrives, because the bear case has already been thought through, and when the market starts making that argument in the stock price, I am not encountering it for the first time.
The goal is not to be a bear. It is to be an honest analyst. Building the bear case first is the most reliable structural intervention I have found for maintaining that honesty when the research process would otherwise carry me away from it.
Disclosure
This newsletter is published for educational and informational purposes only. Nothing written here constitutes financial advice, investment advice, or a recommendation to buy or sell any security.
I am not a licensed financial advisor, investment advisor, broker, or dealer. All analysis reflects my personal research, opinions, and framework as an individual investor. It may contain errors, omissions, or outdated information, and should not be relied upon as the basis for any investment decision.
Investing involves risk, including the possible loss of principal. Past performance, of any security, strategy, or analytical approach discussed here, is not indicative of future results. Markets are unpredictable, and even well-researched theses can and do go wrong.
I may personally hold positions in securities mentioned in this newsletter, either long or short, at the time of publication or at any point thereafter, without obligation to disclose changes. My interests may not align with yours. Always conduct your own independent research and consider your own financial situation, objectives, and risk tolerance before making any investment decisions. Consult a qualified financial professional if you need personalized advice.
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Building the bear case first is a great way to reduce confirmation bias and challenge your own assumptions.
I liked the distinction between a simple risk and a true short thesis; it makes the analysis much sharper.
The focus on identifying early warning signals before investing is particularly practical.
This approach encourages intellectual honesty and leads to more resilient investment decisions.
I wonder how constructing a bear case first, as described, complements dynamic valuation models by ensuring that assumptions about a business's future ROIC are rigorously tested against potential risks, especially during different lifecycle stages.