The way I heard it that makes sense is that to be optimally productive you need to be "hungry" in the sense of wanting more and not being complacent. But you don't want to be starving, generally.

For the same reason, some say the worst addiction is a steady paycheck precisely because it makes you complacent.

These sayings are probably half-motivational with only a kernel of truth. If you are an heir or heiress you will have a big advantage, even if your motivation is less. But there are other metrics than just money, of course. If your point is to achieve excellence or greatness, or operate at the peak of your abilities, then possibly there is such a thing as being too comfortable.