From The Most Important Thing:
…it’s not enough to bet against the crowd. Given the difficulties associated with contrarianism just mentioned, the potentially profitable recognition of divergences from consensus thinking must be based on reason and analysis. You must do things not just because they’re the opposite of what the crowd is doing, but because you know why the crowd is wrong. Only then will you be able to hold firmly to your views and perhaps buy more as your positions take on the appearance of mistakes and as losses accrue rather than gains.