I grew up using a type writer, and a manual one at that. When one was making a carbon or just on a weak ribbon, one learned to strike the keys sharply. After decades of that, I still use my computer keyboard the same way.
Over time, and not much of it, striking the keys hard, plus the fingernails hitting the keys, I tend to wear the legend off the keys. So other than Q,Z,X,and J, my key caps are all blank. My sister once bought me a "lifetime" keyboard, guaranteed forever. Well, it still works, but the paint all wore off.
One old keyboard I had, I wore through not only the paint, but also several keys, like E, I wore completely through the plastic cap. A few keys then had little holes in the key cap.
The other day over at University Surplus, wring bought me a used but like new keyboard. It's a Dell. Looks sturdy. The surplus folks had written "WORKS" on it, so I knew it must work...
I plugged it in, and nothing. The computer makes the Budeep and Bedoop noises when I put the USB plug in and out, so the system at least knows it is there. But no response. Plug the old board back in, and it is fine.
Normally this is the end of my computer ability. But for some reason I had the insight, what if it has to boot up from scratch to use the keyboard. By golly, I plugged her in before powering up, et voila, it works!
There is hope for me yet.