I can't remember the help file off the top of my head (and this may be covered in it already) but, statistically speaking, I find it hard to believe that a skill has an equal chance of improving the first time you use it and the 1000th time. It seems to me that each time I start a run(*) I will be quite likely to get an improvement really early in the run and next to zero improvements towards the end. Anti-spam practice catcher?

(*) - A run can be a practice session against another player, or a practice session against a mob(s), or even a pass of ranking.