What is an idiomatic way of saying that there is no reason to be honest just for the sake of being honest. That is, if you can benefit from a dishonest action and know that you definitely won't suffer any financial, reputational, or other damage that outweighs the benefit, then you should act dishonestly. To put it simply, if you can cheat and get away with it, then cheat.

Is there a common/idiomatic expression for this in English?