Behaviour
Why A Small Win Encourages A Larger Bet
Money that arrived recently and easily is treated as separate from the rest, which loosens the rules an investor applies to what happens to it next.
An early gain rarely stays neutral in an investor's mind. It becomes a distinct pot with looser rules attached, and the size of the next decision tends to grow because of it.
Recent gains get filed in a different mental account
People sort money by where it came from rather than treating it as interchangeable. Wages, gifts and windfalls are held to different standards even when they sit in one account.
Investment gains are filed as belonging to the market rather than to the household. Losing them feels like returning something borrowed rather than losing something owned.
That accounting is not visible as a belief. It shows up only in behavior, as a willingness to risk the gain on terms the original savings would never have been exposed to.
The first result is read as evidence about skill
A single favorable outcome carries almost no information about the process that produced it. Over short periods, results are dominated by market movement common to nearly everything.
The mind is not built for that distinction. An outcome that followed a choice gets attributed to the choice, and the interval between them makes the link feel causal.
The attribution is asymmetric. A gain is read as evidence of judgment, while a loss is read as evidence about conditions, so the running self-assessment only moves upward.
Position sizes grow faster than conviction does
The practical consequence is that stake size drifts. The next purchase is larger, not because the reasoning improved, but because the previous one worked and the money felt available.
Drift of this kind is hard to notice from inside, since each step is only slightly larger than the last. There is no moment at which a decision to increase risk is made.
The result is a portfolio whose largest exposures were set by the sequence of recent outcomes rather than by any view of how much of the total belongs in one place.
Platform design amplifies the pattern
Trading applications report outcomes quickly, prominently and with visual emphasis. A gain is displayed in a way that makes it feel like an event rather than a fluctuation.
Fast feedback shortens the gap between action and result, which is exactly the condition under which behavior is learned most strongly, including behavior that is not producing anything.
Features that make trading easier compound this. Reduced friction means the impulse following a good result meets no delay in which it might fade.
Rules written in advance are the counterweight
A maximum size for any single holding, decided before any results exist, removes the sequence of recent outcomes from the sizing decision entirely.
Rebalancing does similar work automatically. It trims what has grown and adds to what has not, which is the opposite of what a recent win recommends.
Neither device predicts anything about markets. They exist so that the size of a position reflects a considered structure rather than the emotional residue of the last few weeks.
Questions readers ask
Does the witness need to understand investing?
No. Their job is to remember what you said and ask about it. Someone with strong opinions about holdings is usually a worse choice than someone with none.
What if my plan genuinely needs changing?
Then change it through the procedure you wrote down, which normally means a delay and a written reason. The point is to filter impulses, not to freeze the plan.
