You don't lose unless you cash out ....

A good rule of thumb when things are on the upside, in my opinion, is to sell just enough to get back your investment and keep the rest in. If you lose it all, you break even. It's not really a loss. But you want to keep an eye on it and have a trigger that you sell at when you start to see the fall. Some people use 10%, others use 20%. But when the price hits its high then falls that amount below the high, there's your trigger to get out.

For me, I'd rather get a respectable win and lose out on millions than to hold on hoping things will go higher only to see my investment takes a nosedive and lose it all. Greed is a killer.