The fundamentals matter now more than ever. Best of all, the information about how a company is doing is readily available and perfectly legal. Being familiar with a company and how it's doing is not an all-or-nothing game, said Cramer. Even knowing a little bit can still give an investor a leg up on many others. If something changes, how will you know whether to cut your losses or double down? Only homework can answer that question. Homework is not always a guarantee of immediate gains but it is still one of the best weapons investors have in their arsenal.