The market is not a financial instrument. It is a confessional booth, and most people lie in it.
What it actually tests has nothing to do with your model, your thesis, your entry price. It tests your character — specifically, the two rarest and most asymmetric qualities a person can possess: the confidence to stay when you are right, and the honesty to leave when you are wrong.
Most people invert both. They exit at 5% because the profit feels like permission to relax, then watch the position run 150% without them, a ghost at a feast they were invited to. Then they ride a 60% loss into the earth because somewhere around the 6% mark — or the 12%, or the 20% — admitting the mistake felt worse than the loss itself. The portfolio becomes a graveyard of decisions made in the service of ego preservation rather than capital preservation.
This is not a market pathology. It is a human one. The market simply has no patience for euphemism.
And this will happen again. Not occasionally. Billions of times, across every instrument, every cycle, every generation of participants who arrive convinced that they are the exception. The mechanism is that reliable because the flaw is that consistent: people are constitutionally poor at admitting error, and constitutionally poor at tolerating their own success without flinching from it.
The mind required to trade well is not a complex mind. It is a ruthlessly honest one. It says: I was wrong. It says: that's survivable. It says: I will not make the same category of mistake at the same magnitude again. Then it moves.
Simple. Brutal. Almost no one does it.