More than one-third of Americans do not own stocks, and a new BlackRock survey reveals that the holdouts cite a lot of reasons for not being in the market. In its People & Money report published on Thursday, BlackRock listed some of the reasons people who don't invest say they stay on the sidelines. Among the most common are not having enough money, not feeling like they know enough about investing, and being afraid of losses. Those are all fair explanations for not putting your money to work.