After defying gravity for the past couple of years, Palantir Technologies ( PLTR -8.67%) has finally hit turbulence, with the stock plunging as much as 14.9% on Thursday. As of 11:27 a.m. ET, the stock was still down 11.4%.

Related: Walmart, Booking.com will rock markets in a busy earnings week But there was probably more behind the selling, including that Palantir's shares had become way too pricey and were vulnerable to a selloff.

Palantir stock is continuing to slide Thursday as investors weigh a CEO stock sale and potential defense budget cuts. Here’s what you need to know.

Shares of Palantir Technologies ( PLTR -10.08%) fell on Wednesday. The company's stock lost 10.1% as of market close and lost as much as 12.9% earlier in the day. The drop comes as the S&P 500 ( ^GSPC 0.