Long time ago my parents had to sink a new well on the farm... Well, for some reason (We never had this problem in the past) Insects would bet into the pressure switch.. Then I'd have to lift the cover off the well pit (Concrete cover, not an easy lift) turn off power to the well, climb down and clean the switch contacts.. Climb back up restore power, verify operation and re-cover pit.
Do you know why we call errors in computer software or hardware "BUGS"?
Well, Back in the very early days.. ... An insect (Bug) got on a relay contact and caused an error.. Thus ever since, it's been "Bugs".
And remember Murphy's law: There is ALWAYS (at least) one more bug.