Let's first take a look at how Flappy Bird works and how it ended up with its designs. The game is really simple; players control a bird that automatically falls to the ground, and to prevent this bird from falling, players need to touch the screen to make the bird flap upward. There are pipes coming from the right-hand side of the screen, and there's only a small gap left for the bird to go through.

Everything seems so simple, so how did it become so popular? The answer is through simple controls and random generation. The way to control the game is just through a one-finger tap; everything else (like the bird falling down and pipes coming from the right-hand side) is handled by the game. The other factor is random generation.