A mental stop is a decision to exit at a price without an order resting there. Its advantages are real: no visible resting order, freedom to exit on a close rather than an intraday spike, and the ability to judge whether a wick is noise or a genuine break.
Its failure mode is also real, and it is not a knowledge problem. Under loss the brain reframes: the level becomes a zone, the zone becomes a retest, and the retest becomes an average-down. Surveys of blown accounts keep landing on the same cause - a stop that existed only as an intention. See averaging-down and loss-aversion.
A workable compromise: a mental stop for the ordinary exit, plus a catastrophic-stop resting well beyond it as insurance. You keep the flexibility and you cap the tail. If you cannot honour the mental level three times out of three, you do not have a mental stop, you have a hope.
Related: hard-stop, catastrophic-stop, averaging-down, trading-plan