Target date retirement funds are designed to allow investors to pick a simple, all-in-one investment vehicle that automatically adjusts to fit their change in risk tolerance as they approach retirement. However, since the 2008 financial crisis, target funds have been criticized for suffering some huge losses. Since then, the funds have generally been adjusted to reduce risk as an investor approaches retirement, and to continue to make adjustments after the target date is reached. There’s an important lesson to be learned from the market meltdown, though: investors must understand the way their target fund makes investment changes before a big downturn.