Williams P322391 Thermocouple

Why do they continuously fail, the current one didn't even last 7 months, I have other thermocouples on water heaters that are 15 and 20 years old I have some other furnaces thermocouples are possibly 50 years old.

We are not sure why but if one part keeps failing it could be damaged by other component within the unit or outside source(water, voltage etc). Thank you.