Perhaps more interesting, a lot of people I know do train but don't push themselves to the limit. There is always something left in the tank. If their goal is to train to improve it's very [lets say] expensive. They invest a lot for small returns.

Now what if you could keep going if you would otherwise feel the need to quit?

I cycle for a good while then have to guess if ill still be able make it back home. Usually I bet on the safe side. When I bet to low I could add a few laps around the block but this requires an odd kind of discipline that I seem to lack.

Rather than grow it turns into a maintenance routine. If I wanted to do maintenance I would do much less and less frequent.