Your best day can be the reason you fail

Every trader has been warned about the trade after a loss. Revenge, tilt, chasing it back: the whole vocabulary exists, and most people can catch themselves in the act at least sometimes.

Almost nothing warns you about the trade after three wins.

It does not feel like a mistake. It feels like form. The setups are reading clearly, the entries are landing, and the size you were using on Monday starts to look timid by Thursday. So it goes up. Not doubled, and not on a decision you would recognise as one. A little more, because this is working.

The arithmetic of a good week

Take a trader risking one unit a trade and taking about one out when the trade works. Three wins in a row, and the account is up three.

On the fourth, the size is three units, because the read is clear and the week has earned it. The fourth trade loses.

Three wins and one loss, and the account is flat. The week was not undone by a bad trade. It was undone by a good week.

The loss did not need to be a bad trade. At three times the size, it only needed to be an ordinary one.

Why it happens in that order

Sizing up after wins feels like the reward for being right, and it arrives exactly when your evidence is weakest.

A run of wins is the market agreeing with you for a stretch, and stretches end. The conditions that made three setups work are the same conditions that are most likely to have changed by the fourth, because nothing in a market stays generous for long. So the largest position of the week lands on the idea you have the least fresh evidence for, at the moment you are least inclined to look for any.

There is a second reason, and it is the quiet one. Nobody feels the need to justify a size increase that follows success. A trader who doubles after a loss knows what they are doing and usually hates it. A trader who drifts up after three wins is being rewarded by their own account for the drift.

The tell in your own log

It shows up as a number, not a memory. Take a month of trades and write down the risk on each one in the same units.

Now look only at the trades that came directly after two or more winners. Compare that group’s average size to the month’s average size.

If those two numbers are the same, this is not your pattern and you can stop reading. If the after-a-run group is meaningfully bigger, and a fifth is a reasonable rough line to start with, you have found the thing, and you have found it without needing an opinion about discipline.

That expectation goes wrong in a particular direction, and the reason is not complicated: a loss makes people careful and a win makes them comfortable.

What to do about it

The fix is not to stop increasing size. Size should increase, as accounts grow and as evidence accumulates.

The fix is that the increase has to be decided somewhere other than the moment. Write the ladder in advance: the account balance, or the number of trades, or the stretch of results that earns the next step, and by how much. Then a good week cannot promote you, because the ladder already decided when promotion happens.

A prop account makes this sharper than a personal one. Drawdown limits do not care why the size was larger, and a rule that measures your floor in dollars will end an evaluation on the day your confidence is highest, which is a strange sentence until it happens to you.

One line in your plan, and the best day of the month stops being the most dangerous one.