When borrowing from your 401K, the money is removed from whatever investments you have them in. So if the stock market rises sharply, then you lose out on the gains you would have gotten had you left it alone. For example, in 2010 or 2011 (I didn't really pay much attention) my 401K rose something like 25%. So I would have forfeited the 25% on 10K. The next year it rose 16%. Also, if you quit or fired from your job, the loan comes due within 30 to 90 days. If you can't pay, then you have to pay tax on it, plus the 10% penalty. OUCHIE