The more components are used in an electronic appliance, the more factors affect its service life. When designing an appliance, its service life is sometimes defined as being equal to the Mean Time Between Failure (MTBF) of its electronic components.
The service life of the fan, however, generally does not depend on the service life of its electronic components, but on that of its mechanical components. i.e., What matters most is the service life of the bearing part of the motor that rotates the blade. There are various types of bearings, but all Cooling fans use ball bearings for high reliability.
There are two types of life for ball bearings: fatigue life and grease life. Different from industrial motors, the load on fan bearings is comparatively small, so fatigue life is rarely an issue. Therefore, the grease life of ball bearings is the most critical factor for the service life of fans.