To limit one's losses, a stop loss order closes a position at a certain price point/percentage.
Stops are used to limit losses when a trade idea fails.
A stop loss is an important tool in risk management. Any (sensible) book, webinar, mentorship, guru, etc. will stress the importance of using a stop when trading.
Poor stop placement and management can cost you a lot of money, paradoxically.
A candle wick triggers your stop, knocks you out of a trade, and the price proceeds to hit your exact target without you.