The problem with unlimited

If you work out on a weight machine that has a limit--where you have to push the bar until it stops--you're far more likely to to hit that limit than if you had left it to your own initiative to figure out how far is far enough.

People enjoy going to the max (or in the case of Spinal Tap, a little farther than max, to 11). But if there is no max, no limit, it's much easier to satisfy yourself and declare that you've done enough.

If you want your best users to do more, one way to do it is to...