Seriously... what is rng?

WoW is a role-playing game, which means that the outcome to a lot of events is determined by random number (rolling a dice before we played these games on computers).

Random numbers can be your best friend or your worst nightmare, particularly in PvP where a single succesful hit or dispel can change the outcome of an engagement.

We give players the ability to minimize RNG to an extent, such as by stacking hit. Proc abilities in particular can bring a lot of RNG to the table and aren't always something players can adjust around.

Some players want virtually no random number generation in the game (esp. PvP) or at least the ability to opt out of it. Blizzard likes a certain amount of RNG to keep things interesting.