Exercising the switch numerous times will on occasion clean the switch contacts enough to get it to work, some contacts are made of metals that can oxidize over time or you possibly have carbon built up on the contact surfaces from fine wood dust finding their way into the switch enclosure. Wood dust is really fine particles almost like flour which can migrate into really small openings and crevices. Every time you turn a switch off and on an arc occurs between the line and load contact inside the switch assembly, this small arc consumes a small amount of metal and leaves a carbon residue behind, the better quality switches have a wiping function that cleans the contacts each time they are operated, the lower cost switches do not have this feature. Higher quality switches also use silver or gold alloys for the switch contacts that increase the life and reliability greatly.