All things with moving parts fail. Many without any fail. Even wires gradually do exciting things, like grow mm-long nickel whiskers at the solder joints that short out and fry the board.
Most mechanical parts are rated with "Mean Time Between Failure" or "Use cycles." These are valid if you have a pretty constant rate of failure. But many parts experience a 'bathtub' effect. Consider a shiny new widget off the factory: Many will fail in the first month, and the rest will generally last until the cheap capacitors go out in two or three years. The initial failure rate is frustratingly high: Some cheap wireless routers will have to be replaced twice or three times in a fair number of cases, but the ones that survive the first die-off period will serve faithfully for a while.
Clicky switches are vulnerable to some things that negate any claim of durability, especially with dodgy DealExtreme components. ANY water intrusion can brick your switch. If the switch fails open, you can usually jam a wire across the spring and tailcap ring (The part that needs tightening) to get a temporary fix. In some lights this turns a clicky into a twisty, other lights will not turn off reliably. But they'll light, and that's something.