Stock thesis log: write down what would prove you wrong

A stock thesis log is a short record of why someone thinks an investment idea may work and what would make that idea wrong. It is useful because most stock discussions drift toward price targets, screenshots, and confidence. The log pulls the discussion back to assumptions.

This is not a place to tell someone what to buy or sell. It is a way to make a stock idea easier to inspect later.

## Why a thesis log helps

People remember the winning part of a thesis and quietly edit the losing part. A stock goes up and the reason becomes “I saw the trend early.” A stock goes down and the reason becomes “the market misunderstood it.” Without a written boundary, both versions can feel true.

A thesis log prevents that by saving the original shape of the idea:

- what the business or asset was expected to do
- which evidence mattered at the time
- what risk was accepted
- what new fact would weaken or break the idea
- how long the thesis was supposed to take

The most important line is often the uncomfortable one: “I would be wrong if…”

## A compact format

A useful stock thesis log can be short.

1. Thesis: one plain sentence, not a slogan.
2. Evidence: filing, earnings call, product usage, valuation, margin trend, cash flow, sector data, or another checkable source.
3. Position size: not the exact account balance, but the level of risk. Tiny tracker, normal position, concentrated position, leverage, or employer-income overlap.
4. Time horizon: intraday, earnings week, six-month re-rating, multi-year compounding, retirement account, or income portfolio.
5. Wrong-if line: the fact pattern that would make the original reason fail.
6. Review date: when to check again, and what metric should be checked.

The format matters because it separates excitement from evidence. A screenshot of profit is not evidence that the original thesis was good. It only proves that price moved after entry.

## Example without a ticker

Thesis: a company can keep margins stable while revenue slows because its subscription mix is improving.

Evidence: last two quarterly filings show subscription revenue growing faster than total revenue; gross margin did not compress.

Position size: normal position, no leverage, no employer-income overlap.

Time horizon: two earnings cycles.

Wrong-if: subscription growth falls below total revenue growth, or margin compresses for two quarters while management still calls it temporary.

Review date: after the next earnings call transcript and filing.

This kind of note does not need a price target to be useful. It gives the later reader a way to ask whether the reason still exists.

## Common failure modes

The thesis is just a price move: “It is down a lot” or “It is breaking out” may be a trade setup, but it is not a business thesis.

The evidence is social proof: “Everyone on the forum is talking about it” is a sentiment signal, not a source.

The time horizon is missing: a good one-week setup can become a bad long-term position if the holder changes the story after the fact.

The wrong-if line is impossible: “I would be wrong if the company goes bankrupt” is too late to be useful. The line should trigger before the entire idea has already failed.

The position size is hidden from the logic: a risky idea can still be acceptable as a tiny tracker. The same idea can become reckless when it is concentrated, leveraged, or tied to the investor's salary source.

## Reusable rule

Before arguing about whether a stock idea is smart, ask whether the thesis can survive being written in six lines. If the idea cannot name evidence, time horizon, position size, and a wrong-if line, the discussion is probably still at the hype stage.

Stock thesis log: write down what would prove you wrong

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