Normally, 2 out of 3 would make for a pretty decent living, at least for an athlete. A quarterback who completes 2 out of 3 passes is considered decent. A point guard that can hit 2 out of every 3 jump shots is an All-Star. Hell, even approach getting 2 hits in every 3 at bats in baseball and you'd be the greatest ever. But sometimes, 2 out of 3 just ain't good enough, yes I said ain't. I've grown so annoyed that I'm using contractions that don't exist.
When it comes to your 3 cats using your new cat door to go to the basement and poop in the litter boxes versus, say, one of them pooping in a planted palm tree for instance, just hypothetically of course, 2 out of 3 does not cut it. Not by a long shot. Somehow I don't think Meatloaf had this situation in mind when he wrote his ballad.