Well, you shouldn't. The whole idea with retirement accounts is that they aren't fun money for investing whims or when you get jealous your neighbor has a new mercedes and you don't.

The only time money should be pulled out would be for a serious emergency and even then as a last resort its pretty stupid as bankrupcy would make more sense as bankrupcy courts can't go after your 401k.

If you're regularly pulling money out of your 401k then you're doing retirement planning wrong.