Stick drift on a controller is when one of your analog sticks moves on its own, even if you’re not touching the controller.
This will interfere with playing games, as it will move your stick and alter movement / aiming etc.
There are actually a few different factors that can cause and contribute to stick drift. From something as small as a speck of dust or a crumb could get in the way of the electrical current flowing. Other common stick drift causes include wear and tear as well as manufacturer error.
Controller drift can be due to one of two things:
The analog stick is dirty.
The analog stick or the potentiometer is damaged.
You can expect general wear-and-tear from frequent use. If cleaning the controller doesn’t fix the problem, you should look into getting your controller replaced or repaired before disassembling it.