There's a moment inside almost every losing session that decides how bad the day actually gets, and it isn't the moment the first trade goes red.

It isn't the setup being wrong, because the setups earlier in the day were often fine.

The market didn't turn hostile either, because the same conditions get traded clean by someone two seats over.

It isn't even the size of the trade that finally breaks the daily limit, because that one usually matched the plan too.

It's the trade that comes right after the limit is already gone, the one that somehow doesn't feel like a new decision at all.

One prop firm that tracks its own funded-account failures put an exact number on how often this single behavior is the reason an account gets shut down: 78.7%.

Not a bad strategy. Not one catastrophic trade. It was crossing a line that had already been drawn, in writing, before the session opened.

Psychologists gave the moment a name, and it has nothing to do with trading.

It comes from research on why people who've spent a long stretch making decisions become the worst possible version of themselves for the one decision that actually matters.

Traders who've never heard the term are living inside it every session, at the exact minute they need their own rule the most.

A simulation built for this report ran 20,000 modeled trading days through two versions of the same trader, one that stopped at the line and one that didn't, with nothing else changed.

The two averages came out almost identical.

The difference wasn't in the average at all. It was in how often an ordinary bad day turned into a genuinely bad one, and that number climbed every single time one more trade got added.

All of it, the 78.7%, the psychology behind it, the 20,000-day simulation, and the exact dollar math on what one more trade costs, is laid out below, with the page number where each piece lives.