Gamers like to criticize "RNG" in games. For example, picture a game of dice where you and your opponent both roll a dice, and the highest roll wins. That's "pure RNG."

Random Number Generator

A random number generator (RNG) is an algorithm that produces random numbers. In video games, these random numbers are used to determine random events, like your chance at landing a critical hit or picking up a rare item.

Random number generation, or RNG, is a defining factor in many modern games. They're the reason why you always meet unique Pokemon, why items in Mario Kart are different each time you pick them up, and why you randomly find super cool treasure (or not) in Diablo. Some procedurally-generated games, like The Binding of Issac or Minecraft, wouldn't even be possible without RNG.

Not every game depends on RNG. Rhythm games like Dance Dance Revolution or Guitar Hero are a great example. Competitive multiplayer games like Rocket League and Mortal Kombat are practically devoid of randomness, too.

This isn't to say that all competitive games avoid RNGs. Counter-Strike: Global Offensive uses RNG to determine how bullets hit targets, and DOTA 2 uses RNG to determine how often abilities will affect opponents. There's an element of randomness in the gameplay, making it unpredictable.

RNG Keeps Games Fresh (But Can Undermine Skill)

Randomness is what keeps things from becoming monotonous. It's what leads to curiosity and risk, and it's one of the best tools to keep a game fresh.

Think of the blocks in Tetris. Each block in Tetris is chosen randomly. If they weren't, then Tetris wouldn't be fun, stressful, or unpredictable. There would be no risky or clever moves; there would only be the right move. Tetris would be an endless memorization game---like counting down the digits of Pi.

Even some competitive games, like Hearthstone, rely heavily on risk-based mechanics that are more comparable to Yahtzee than they are to Mortal Kombat. And that's where RNG becomes a contentious subject. In an RNG-heavy game like Hearthstone, skill can take a backseat to luck. A lucky novice can beat a pro. So what happens when you stick RNG in other competitive games, like CS:GO or DOTA?

You end up with a lot of pissed off gamers. While randomness in a fighting game may sound like fun to you or me, some competitive gamers are (understandably) turned off by the idea of losing to lady luck. Imagine if people took a straight competitive game, like chess, and added something like random power-ups. In the mind of chess fans, this completely defeats the purpose of chess. A gamer who loses might blame a loss on the "RNG" that went in their opponent's favor.f

Some RNG Can Be Manipulated

As we mentioned earlier, random number generators are algorithms. They're basically just math problems that spit out random values. But as you know from your many years of math experience, two plus two always equals four. For an algorithm to produce random values, it needs to include variables (like X or Y).

Where does a video game get its variables from? It has to look for naturally changing local values. A game could use the console's internal clock as a variable, or the number of objects on screen, or your character's name, or even the sequence of buttons that you've pressed since starting the game. There are many ways for a computer to generate random numbers.

In some cases, these numbers are actually predictable enough to manipulate. It's a bit like counting cards, except harder.

RNG manipulation isn't a part of competitive gaming, but it's a part of classic RPGs and retro video games (where "RNG" algorithms were fairly straightforward). An experienced gamer can count their way into a perfect Pokemon or press seemingly random buttons to get rare items in Final Fantasy.

RNG: Good or Bad?

For many people, RNG is great for keeping games unpredictable and fresh. Random number generators are a crucial part of the gameplay in many modern puzzle games, card games, and RPGs, and they've been used to good effect in some action and multiplayer games.

RNG can be good. Should every Minecraft world be the same, or should every item you find in Diablo be identical every time you play? RNG offers variety and can keep things fresh.

But many competitive gamers feel that RNG undermines skill. It can be an annoying complaint to hear, but it's only annoying because some competitive games, like Smash Bros, lead a double-life as casual party games (which require RNG to stay fun). Games made for the esports community might place a heavy emphasis on skill-based mechanics for this reason.

Related: What Are Esports, and Why Do People Watch Them?