If you can't come up with the bucks, the IRS will tax the money. If you're under 55, they'll also zap you with that 10 percent penalty again - and you can't say no to the tax man. That's a heck of a thing to face after losing your job. The rules get a bit complicated here, so you might want to chat with your company's employee benefits person. They're aghast at the thought of it.
Planners are a Calvinist bunch.
If you get in the habit of raiding the sacred piggy bank, you may retire barefoot to a tar-paper shack. It teaches them bad habits. You can never borrow more than half your 401, and some plans won't let you borrow at all. Home-equity loans have their own pluses and minuses. So a rate of 10 percent shrinks to a bit under 7 percent for a middle-income family.