Why was sticky key introduced?

When we press Shift many times a pop up comes i开发者_JAVA百科f sticky key should be activated.. Whats the use of it?

Disabled people who cannot hold down two keys simultaneously. Hit Shift, hit your key, boom! Just like hitting Shift+key, but could be operated with a stick from your mouth. Or one finger.

It's an accessibility feature for people who can't use two hands at once. For example, those with no arms, or immobile arms have to type using a single stick in their mouth.