I am hoping that I can boil down a discussion that has been going on outside the forum for over year into a few lines.
RPGs in general have skill progression in a linear curve*. Your character spends or gains experience as a gradual progression. +1 to +2; 30% to 32% and so forth.
However, the thrust of thinking at chez Walsingham has been that progression in real people doesn't go this way. it is less of a curve and more of a staircase. For whatever reason (and there has been a LOT of debate on this) the effective capability of people/trainees etc. tends to move in bursts. They achieve