So how do you know whether you should invest in a given token sale? Eric Ervin. You have made a profitable trade, but as always, the moment you sold, the coin runs up again. The problem is that since derivatives trading is a zero-sum game, there is always a winner, but more importantly a loser. For each position, we must set a precise target level at which to take profit and, more importantly, a stop-loss level for cutting losses.