Judging a decision by how it turned out rather than by the information available when it was made. It is the single most expensive habit in poker, and the hardest to see in yourself, because the feedback the game gives you is genuinely misleading.
The problem is structural. A correct call can lose, a reckless bluff can win, and in the short run the outcome tells you almost nothing about the quality of the reasoning behind it. A player who folds a strong hand to a bluff and sees the cards will remember the fold as a mistake. A player who calls off a stack on a hopeless draw and hits will remember it as a read. Both memories are wrong, and both will be acted on for weeks.
The correct frame is to grade the decision on what was knowable at the time — the opponent's betting sequence, the board, the price, everything you had actually observed at the table — and then to ignore the river card entirely. A hand where you extracted the maximum and still lost is a hand played well. A hand where you got away with a bad call is a leak that happened to be paid off.
The practical test is simple: describe the decision without stating the result. If it still sounds right, it probably was. If the only argument in its favour is that it worked, there was no argument.
This is also why a review that begins with who won the pot is close to worthless.