% Chance to increase potential tier?

I hate when people say this on any thread about probabilities. Of course it's random but there is still a set chance of it happening.

I did not challange the numbers at all with my post, I simply pointed out that the random factor and/or unknown variables play a big role in cubing. We have not a clue if there is simply a set percentage or more to it than that. Granted, luck might have been a bad coice of wording.