If you are a heavy user (using it for more than 10 hours a day),
then the estimate lifespan is 2 years or perhaps shorter.
If you spend less than 2 hours with your computer, the estimated
lifespan is high. I've got a mouse which lasted me 5 years when I
was too busy with studies to use the computer.
In most of these cases, a USB mouse spoils faster than PS/2 mouse,
I have no idea why. It could be the speed, as a USB technology is
faster than PS/2 technology.
Wear and tear is one reason why a mouse can't last long. Those who
mistreats their mouse (like banging it when it's not working), will
not get it to last long either.
