In this Rule Breaker segment, Motley Fool co-founder David Gardner shifts the focus away from the numbers game to a mental one. Picking good investments is, after all, only one part of growing your wealth — another key aspect is maintaining the disciplined mindset and emotional distance required to avoid making the wrong moves. Here, he goes back to one of his favorite pieces of advice — or perhaps a market truism. And it’s one that holds something of a contradiction in it.