This game relies on random number generation for almost everything. Without going deeper in the mathematical and statistical theories behind random numbers, suffices to say that for a game, a sequence of number that repeats once every trillion times is more than enough for the playtime of any person.

In PoE every map is random, with the exception of some key points. Each time a player plays a map, the map is randomly generated with random placement of enemies so that it'd take trillions of runs for the same layout to repeat itself. That is the foundation of Action RPGs because the players are going to replay the game many times to get higher levels and higher grade items. If not for random generation there would be huge labour in building variations for every area by hand. On the other hand, care must be taken with the rules of random generated maps to avoid generating maps with impossible paths, blocked paths or enemies that are locked in islands for example.

Often, in this game, randomness is excessive. For example: to go in the mines the player needs fuel and the fuel is random. The player can't predict when fuel spawns in a place, it's luck based. The properties of all items are randomized, with trillions of combinations. There are items that modify properties of others, shifting numbers, adding or removing properties. Those modifiers are mostly unpredictable with some rare exceptions. Sometimes the player desires a certain property but the probability is around 1% or even lower. That means that the player has to make thousands of attempts until he or she gets what they want. Randomness like that frustrates the player because they don't know if they are going to be successful after ten or ten thousand attempts.

Randomness in this game is tied to the fact that the player has to invest many hours in it. If something has a very low probability there isn't much that you can do other than spending more time to try again. In addition, this game's business model does not charge players for anything except cosmetics and more storage space for items. To the eyes of the company it's desirable that players spend as many hours as they can playing their game.

According to the game's director the randomness factor is intentional. Everything, except for the plot, is random. The quantity of rare items in the mines is high and to limit the number of times the player can go in there they made the fuel random. There are many other challenges and mini games that reward the player with valuable items and all those mini games and challenges are random. The player can't predict which one they are going to encounter in a map. They made it that way to prevent the players from overplaying one challenge or mini game and exhausting it. The player can skip those challenges or mini games if they aren't willing to play it, but they can't choose when they are going to play it. There are many players who criticize this approach.

Could time be used to limit players instead of randomness? The problem with time is that some players have much more free time than others, some may play 2 hours a week while others may play 40 hours a week. It's not possible to use time in the way Candy Crush does, where one life is given for free every 30 minutes, for example. Randomness is the only thing that is equal for everyone. In other words, this game has the same logic as a lottery.

What do Sonic, Tomb Raider, Duke Nukem, Mario, Mickey Mouse, Jedi Knight, Doom, etc have in common in regards to obstacles? Time is constant. Every time a game presents gears, moving platforms, closing doors, spikes, crushing ceiling, etc there is a fixed time interval.

If an obstacle made of spikes or a lava jet have randomized frequency, damage, speed or height the game ends up punishing the player. The player isn't required to learn something and their progress is about being lucky. Having obstacles that have no regular pattern leads to frustration. The player feels punished rather than rewarded. Imagine a password that for every wrong input it changes to a random value. An obstacle like this is impossible to solve.

A level may have obstacles that have a random behaviour but the time of activation must follow a pattern. Otherwise two extreme conditions can happen: either the winning condition is trivial or the obstacle is impossible to pass.