The rapid transition from defined benefit (DB) pension plans to defined contribution (DC) plans has a potential benefit of offering pension holders greater control over how their pension accumulations are invested. If pension holders are willing to take some risk, investments in the stock market could increase their economic preparation for retirement, and, indeed, economic theory as well as the typical advice of financial advisors calls for stock market investments. Yet, the rate of stock holding is much below what theory suggests it should be, undoing any benefit associated with the greater control coming from DC plans. The leading explanations for this under-investing include excessive risk aversion, costs of entry, and misperceptions about possible returns in the stock market. We show that excessive risk aversion is not able to account for the low fraction of stock holding. However, a model with heterogeneous subjective expectations about stock market returns is able to account for low stock market participation, and tracks the share of risky assets conditional on participation reasonably well. Based on the model with subjective expectations, we estimate a welfare loss of up to 12% compared to investment under rational expectations, if actual returns follow the same distribution as in the past 50 years. The policy implication is that there is considerable scope for welfare improvement as a result of consumer education regarding stock market returns. However, the welfare loss is much smaller if individuals are not very risk averse or if actual returns follow the same distribution as in the past 10 years.