One of the key insights of the CAPM is that it answers an important investment question: "What is the expected return if I purchase security XYZ?" The assumption that Sharpe built into the model is ...

Barberis, Nicholas, Robin Greenwood, Lawrence Jin, and Andrei Shleifer. "X-CAPM: An Extrapolative Capital Asset Pricing Model." Journal of Financial Economics 115, no. 1 (January 2015): 1–24.