This view that market knows the best is actually quite misguided. Market does prices assets correctly after long enough period of time but it oscillates and bounces a lot before that happens. It's wrong to say that any point in time market knows the best and current price are exactly the fair price. If this was true, asset prices simply don't keep swinging 10% for days on. Gold isn't worth $100 at 9 AM and suddenly becomes worth $70 at noon.