Just like people, garage doors need periodic checkups to make sure everything is in good working order for the upcoming year or two.
So where a doctor might check your throat and in your ears and up your nose, a garage door repair person might have a look at the cables, the springs, and the rollers. Where a doctor might decide to give you some main medication, a garage door services person would lubricate some moving parts and tighten up the hinges and tracks, the hardware. And where you might have your eyes checked up, so would a garage door! The sensors of the reversal mechanism are somewhat like laser eyes, and they need to be in good working order in order for it to function correctly an safely.
And just like people's backs might go out, it's also pretty common for a garage door opener to lose its drive gear- either the chain, the belt, or the screw gets old and wears out. And that doesn't necessarily mean you need to replace the entire opener- just the one part will do.
And just like your knees might go out (or one other the other), one or the other of the springs of a garage door are liable to wear out and have problems.