Palantir has been one of the best-performing S&P 500 stocks this year.Palantir Technologies (PLTR -0.83%) has been a genius investment this year. The stock is up over 140%, placing it in the top five best-performing stocks in the S&P 500. However, with a run like that, many investors may be questioning whether right now is a good time to invest in Palantir. I think there's one primary reason that makes it clear what investors should do, and it's only a matter of time before Palantir's stock makes a sizable ...