Marginal Cases Don't Matter

Most decisions are overdetermined. In most situations, the expected benefits clearly outweigh the expected costs or the expected costs clearly outweigh the expected benefits. Should you exercise? Yes. Should you light yourself on fire? No.

If there is a cheap way to find out what the right choice is then you should do that. Suppose there is not. What if you already did your research and it is still unclear what choice you should make?

If the expected benefits of a choice do not clearly outweigh the expected costs of the choice then that implies the expected benefits approximately equal the expected costs. Thus, the net benefit of making the right choice is approximately zero. It literally doesn't matter if you make the right choice.