"The ideal is obviously to exit all trades with a profit, but that is not always realistic. Using a protective Stop Loss will help you ensure that losses and risks are limited."
"Yes dad!"

Diversify your portfolio to reduce risk!
If you invest in things that do not move in the same direction, at the same time or at the same pace, then you will reduce your chances of losing all of your money at the same time or at the same pace. Simple as that.