A stop-loss is not an admission of failure; it is the price at which your reason for the trade is proven wrong. The single biggest stop-loss mistake is placing it based on how much you are willing to lose ('I'll risk $100') rather than where the setup is invalidated. Get this backwards and you will be stopped out of good trades by normal noise, again and again.
Stops go at invalidation
Place the stop just beyond the level that, if breached, means the trade idea is wrong: below the higher low in an uptrend, beyond the pattern's edge, past the structure point. Then — and only then — calculate position size so that distance equals your fixed risk (the previous lessons). The market decides where the stop goes; your account decides how big the position is. Never move a stop further away to avoid being stopped out — that is how small losses become catastrophic ones.
Give it room with volatility
A stop placed right at an obvious level often gets hunted — recall the liquidity lesson: stops cluster just beyond swing points, and price is drawn there. Placing your stop a small ATR buffer beyond the level, rather than exactly on it, helps avoid being shaken out by a stop-grab wick before the move goes your way. Wide enough to survive noise, tight enough to keep risk defined.
Discipline over hope
The hardest part of stops is honouring them. Moving a stop, or removing it 'just this once' because you are sure price will come back, is the classic account-killer — it converts a planned 1% loss into an unplanned, unbounded one. A stop you will not honour is not a stop. Decide it before you enter, set it, and let it do its job: the whole point is to make your worst case known and survivable.