Most of the good reasons against borrowing have already been listed: losing growth opportunity, potentially at risk if the job ends, may not be able to contribute while paying it back, etc.
One that's been mentioned on this thread though, but is somewhat inaccurate, is the belief that you're "paying tax twice" on money borrowed from a 401k. At risk of sounding pedantic, I think it's worth busting that myth. The only thing that's taxed twice is the interest paid on the loan. The principal amount, is taxed once--and only once--at the time of withdrawal from the account.
Yes, a 401k loan is paid back with post-tax dollars... just like any other loan would be. A thought example that makes it more obvious, suppose you take a $1,000 loan from a 401k... then stuff that cash in your mattress. You then use that cash from the mattress to pay the loan back. No extra tax was paid.
Anyway, with the "never say never" phrase still important, I'm not in any way saying that a 401k borrow is a good idea. I just hate to see misinformation used to justify the decision
