Humans compress data into stories. Markets produce enormous quantities of near-random data, so the story machine never stops running. Every close has an explanation by evening, and the explanation is often fitted to the move rather than the other way round.
The trading cost is confidence. A trader with a story holds longer, sizes larger, and dismisses contrary evidence, because the story has become the position. Financial media is a story factory, and reading it after a loss is how a temporary drawdown turns into a conviction bet.
Test the narrative by asking what the same story predicted last time, and whether you would have traded it in advance rather than after the fact. Stories that only work in hindsight are decoration.
Related: hindsight-bias, availability-heuristic