A successful investor is not always perfect, there are some successful people come from failed investment experience and at least get their money back with no profit. some investment will never happen without failure, this is an anti-mainstream procedure. If you kind of people who play safe, you will only feel successful in one way, nothing more.
losing is not important, but how you handle that loss is important.
lets say you have bought Dash yesterday at 0.04BTC price and wanted to make profit but price started going down and finally reached 0.03BTC as of today. if you just blindly wait and hope for profit you have already lost in trading and better stop doing it.
but if you start acting more logically and sell at 0.039 for instance to prevent more losses and buy back at the bottom if you still think it can rise.