The question is only whether there's a real pattern here, despite the exceptions to it. These social patterns are always ceteris paribus. There are always exceptions. But do nice guys (as in sensitive idealists) tend to finish last in business, politics, and romance? Is there a real pattern there, and if so, how should we explain it? I explain it by linking idealism with a type of real-world incompetence.

I'm not the source of the idiom that nice guys finish last. The idiom likely caught on because there's a kernel of truth in it.