Which is about the same time I decided the opposite, having been burned a couple times. You're neglecting the amount of time and effort other people in the group put in to make a new employee productive. Where I work it takes an absolute minimum of about three months to understand how all the moving pieces of the business data flow fit together, and maybe another three before the new person is truly independent.
And during that time other people in the group are spending time on the new guy instead of doing work themselves. If I hire someone and then he quits in six months, all that effort is wasted.