The equity premium puzzle is a mystery to financial academics. According to some academics, the difference is too large to reflect a "proper" level of compensation that would occur as a result of investor risk aversion; therefore, the premium should actually be much lower than the historic average of 6%.
More recent extensions to the puzzle attempt to offer a different rationale for explaining the EPP, such as investor prospects and macroeconomic influences. No matter the explanation, the fact remains that investors are being rewarded very well for holding equity compared to government bonds.