When you do not know a thing, to allow that you do not know it--this is knowledge.
Investing is a big bet on an unknowable future. The mark of wisdom is accepting just how unknowable it is. Granted, that's not easy. Our brains are built to think the future will be like the near past. And we're too ready to act on the predictions of pundits, who are no more clued in than we are about what lies ahead.
Being humble in the face of uncertainty keeps you from costly mistakes. You won't jump on yesterday's bandwagon. And before you invest, you'll be more likely to ask a key question: "What if I'm wrong?"