Explain the following paradox. A put option is a highly volatile security. If the underlying stock has a positive beta, then a put option on that stock will have a negative beta (because the put and the stock move in opposite directions).

According to the CAPM, an asset with a negative beta, such as the put option, has an expected return below the risk-free rate.

How can an equilibrium exist in which a highly risky security such as a put option offers an expected return below a much safer security such as a Treasury bill?