User blog comment:Krufix/Randomness fix possibility/@comment-66.30.32.89-20120409015728

If you don't want full random, just go with pseudo-random distribution from DotA. Although, I don't think Riot would have the time to recode the entire chance system to scale it with pseudo-random.

Pseudo random in a nutshell: Your given % chance to proc X is the average chance to proc overall. You start with a low chance to proc and for each hit without proc-ing, the chance increases. On proc, reset chance. This reduces the chance of getting two lol-crits in a row and reduces the chance of getting 0 procs in 10 hits. It also has a threshold of when you are guarenteed to proc, but that cap is rarely reached.