Joy-Con drift

This takes the joy right out

Joy-Con drift is an issue where the analog sticks on the Joy-Cons (the main controllers used for the Nintendo Switch) are exposed to dust, causing the system to detect analog stick movement that isn't actually happening.

What Made This Worse

Nintendo claims that this is not a real issue and has not re-designed the Joy-Cons to fix it. All they've done about this is offering repairs, which tend to last only a few weeks before drifting happens again. What's worse is that they are receiving a number of lawsuits for that issue.
The Switch Lite has the same issue, and since it's Joy-Cons aren't detachable, you need to send in the whole console to have it fixed.

Ways You Can Fix This

Blow the dust off using compressed air or straw.
Go into the controller finder menu on the system and hold down the button for the Joy-Con that's drifting until it's battery runs out. Then dip a Q-Tip in isopropyl alcohol or a hand sanitizer, hold the analog stick all the way to edge, and rub the Q-Tip in the center underneath the analog stick. Do a few full rotations and let the alcohol dry out before recharging the battery.
Go into the controller finder menu on the system and hold down the button for the Joy-Con that's drifting. While the Joy-Con is vibrating, do a few full rotations of the analog stick.

Redeeming Qualities

The pro controller, the GameCube-styled controller, or any of the third-party ones do not have this issue.
This can be fixed if you do any of the following steps mentioned above.