You, your employer and your plan's investment managers fail to follow even the most basic rules of investing. You overtrade, chase performance, do not think long term. All of you - All Of You - have done a horrible job managing your retirement plans.
Owning a variety of asset classes means that some part of your portfolio will be doing well when the cyclical turmoil arises. A broadly diversified portfolio includes large capitalization stocks, small cap, emerging markets, fixed income, real estate and commodities.
Hedge funds are not especially liquid. Many are 'gated' - meaning there are only small windows when you can withdraw your money. They typically have a high minimum investment and often require investors keep their money in the fund for at least one year.