A stop loss is the price where you admit the trade is wrong and get out. You decide it before you enter, when you are calm, because in the moment your brain will invent reasons to hold a loser.
Place your stop at a level that, if hit, means your idea was actually wrong, not just at a random round number. Then size the position so that loss is small.
Key takeaway
Pre-decide your exit. A planned small loss beats an unplanned large one every time.