I think that is a chance i am willing to take, if i invest 1 bitcoin and i get 3 bitcoins back, and i reinvest one bitcoin, i already have my investments back, so even if i lose the remaining bitcoins, it does not matter anymore because i have already made my profit
Unless you invest 1 bitcoin in a site and get nothing back.
Sometimes, if you invest first, you might get something back. But there's still sties that don't pay anything to start with.