From Diablo Wiki
RNG = Random Number Generator.
This acronym is commonly used when referring to random item finds in games like Diablo III. Players say things like, "No legendaries all day. The RNG is kicking my ass."
- More Reference terms.
 Official Remarks
Vaeflare: The Keywardens all have the same innate drop rates. So, as some players in this thread have already mentioned, the variation you’re experiencing is due simply to the nature of RNG. The only MP strength in which the keys and organs are guaranteed to drop if you have a full five stacks of Nephalem Valor is MP10 (100% drop chance).
It was too good to be true
Don’t know why blizz had to nerf the drop rates again. It’s almost back to 1.0.4 levels. I’m talking about legendary and set items. Yes, I farm a lot non stop, and I can honestly say something is different. When the patch launched, I was running the same thing and I would get at least 1 legendary per run, or 1 every 2 runs. Same goes with my friends, none of them are getting any legendaries now, and they farm a lot. I farm the same amount of time each day. usually 8 hours. Today been farming 6 hours, still 0 legendaries, 0 sets. Lylirra: Item drop rates do not Deep Breath more, guys. =/
- We haven’t made any changes to drop rates or drop quality. - They are same as they were yesterday, when the patch went live. - We implemented some hotfixes this morning, but they weren’t related to items at all. - Those changes can be found here.
In all likelihood, you’re just experiencing normal RNG. If, however, you feel like something may be bugged, go ahead and drop a line in the Bug Report forum so we can investigate.
Just out of general interest.. Will we be able to type /roll in-game and have a random number between 1-100 pop up? Might be useful for some situations.
I think it could actually be useful in cases where you’re playing with … say, two barb friends and some amazing axe drops they’d both want.
THATS RNG BROI haven’t heard of any intent to implement, but I sort of like it… so maybe I will use one of my Diablo III wishes.
 Random Number Generators
Programming a truly "random" number generator is actually quite a difficulty challenge and the history of human efforts (and notable failures, such as in lotteries) to create an RNG makes for an interesting read. Many things we call "random" are actually not, often by design. A quote from the wikipedia RNG article:
- Some applications which appear at first sight to be suitable for randomization are in fact not quite so simple. For instance, a system that "randomly" selects music tracks for a background music system must only appear random, and may even have ways to control the selection of music: a true random system would have no restriction on the same item appearing two or three times in succession.