In many MMOs players character progression is artificially capped, e.g. by level 60 or 90 or 100 or whatever. Why do MMOs have these level caps in the first place? Why not just allow characters to continue to arbitrary levels with a mathematically designed leveling system that keeps the leveling experience interesting and endless? Answers to this question may help us to see the reason behind the feature and decide if and how this should be implemented in our MMOs.