Nvidia's future should be even more exciting than its present.Why should you not invest in Nvidia (NVDA -0.12%) right now? You'd definitely be late to the party buying shares of a company with a market cap of $4.2 trillion. Other stocks could have better growth prospects. Nvidia is also expensive, with a forward earnings multiple of over 38.I'm not going to focus on the bear case for Nvidia, though. The bull case looks even more compelling. Here are five reasons to buy Nvidia stock like there's no tomorrow. ...