Don't use much money if you are not prepared to lose. That's something they have to remember. Only use money they can afford.
I would say that "dont use money if you are not prepared to spend them". I will get back to my losing=spending vision. Lets take two activities, gambling and lets say bowling. Both activities are for entertainment, for having fun. We have lets say similar budget, $30. We place bets, win or lose, get fun or feel unhappy. We throw ball, his strike or miss, get fun or feel unhappy. If we put this situation on OP question, then he is doubting that missing bowling pin is fun, however people keep playing bowling.