Open up the next switch that craps out. Youll see where they keep failing. Its usually overtime the contacts get further away causing arcing which overheats them to the point they weld themselves stuck on. Or they no longer can make contact.8-10 a year wow, more like every 4 years for me. However I do change a lot of the switches, they burn easily and I don't know what causes it, this month I have changed 3x, it takes few minutes to change at the job, not that bad or expensive.