There's an entire system organized around the idea that we're too weak to deliver effort without external rewards and punishment. If you only grow on demand, you're selling yourself short. If you're only as good as your current boss/trainer/sergeant, you've given over the most important thing you have to someone else.
The thing I care the most about: what do you do when no one is looking, what do you make when it's not an immediate part of your job... how many push ups do you do, just because you can?
