The list of billionaires who haven't sold Palantir recently is unsurprisingly long.Only eight members of the S&P 500 (^GSPC +0.54%) have delivered year-to-date gains of more than 100%. Palantir Technologies (PLTR +1.62%) is one of them.However, the luster of this high-flying artificial intelligence (AI) stock has been somewhat tarnished lately. In recent weeks, Palantir's share price has pulled back roughly 20% below its all-time high set in early November.But while many investors are selling Palantir stock ...