That said, the theory behind CAPM is more complicated ... The cost of equity can mean two different things, depending on who’s using it. Investors use it as a benchmark for an equity investment ...

Greenwood, Robin, Mark S. Seasholes, and David Biery. "The Portfolio Improvement Rule and the CAPM." Harvard Business School Technical Note 216-027, October 2015. (Revised February 2016.) ...