Nice.

As often happens with maths, it's funny how a rather arbitrary feature of our body, determines our mathematical understanding of the world so strongly. But I do prefer owning that arbitrariness instead of fighting it.

I had a similar though with respect to money, and it's also funny on that realm that different thresholds become crossable with time. So that even if you get stuck on one (let's say you can't hit 1 million), as long as you persist or remain static, the challenge will expire and you will automatically be placed in the next round.

Also if you decide to go with the linear scaling approach, (say, going from 100k to 1M by doing the same thing more often), each time the duration of each level will increase, until you retire.