Ok,
here is the thing with programmed randomisation. It is not possible. What we have in Games is as somewhere mentioned above, a pseudo-random number generator. Computers calculate the numbers and you cannot calculate true randomness. So we get something that is nearly random. It is like those calculations you (hopefully) had in school with the funny lim->0 or lim->infinity.
That's a bit of an easy explanation but should suffice here for mere understanding.

Those RNGs tend to get streaky sometimes. I guess everyone playing games has expirienced this at some point. Fun fact is that with true randomness even that would not be impossible. So it usually works out. Streaks are very annoying when playing though. I guess that is why they created that loaded dice option. I have not looked into that but i think they flatten out those streaks with it somehow. That again goes farther away from RNG.

That is my knowledge so far. If there is some math student around they may have a better explanation on propability calculation than i have.