A stop-loss is not a "loss" or "mistake," but an "insurance premium (necessary expense)" paid to stay in business in an uncertain market. Markets always contain noise; closing small is part of a great strategy.
Probabilistic Basis
No matter how strong your statistical edge, probabilistic runs of unfavorable outcomes are unavoidable. What matters is staying able to play again (capital and mental), not being right each time. A preset stop order is the most proven way to remove in-the-moment emotional decisions.
Iron Rule
Decide "exit if it breaks here, invalidating the thesis" before entry, and never move that line emotionally after the fill.