Classic examples are head-and-shoulders, double-top, triple-top, rounding-bottom and island-reversal. Each describes a trend losing its ability to make new extremes, followed by a break of the structure that had been holding.
Reversal patterns are almost always defined with a confirmation level, most often a neckline, and they are not considered complete until that level breaks. Acting before confirmation means guessing at a top or bottom, which is where most of the damage in trading gets done.
Even confirmed, they fail regularly. A failed-pattern frequently produces a violent move the other way, because everyone positioned for the reversal is stopped out at once. Size the trade so that being wrong is survivable rather than assuming the pattern will work.
Related: continuation-pattern, neckline, double-top, failed-pattern, head-and-shoulders