We should be aware of the difference between reliability and durability. Reliability revolves around random failure rates, durability is about aging mechanisms. In most cases, both are very low for electronic systems.
In fact only a few electronic components have known aging mechanisms: electrolytic capacitors, LEDs, FLASH memory, switches, connectors, and so on. Likewise, failure rates for almost all components is astonishingly low.
The big exception is electrical and/or thermal stress. Operating components close to, or beyond, their safe operating area increases the random failure rate and any aging mechanisms. I should also mention thermal cycling, even when it is within the specified temperature range for the component. It can loosen lead-offs from integrated circuits, or cause encapsulation failures. Finally, mechanical vibration can cause fatigue failures in component wires.
So the secret to a long and reliable life is to ensure that all components are operated well within their parameters, don't subject them to unnecessary thermal cycling (so manage heat extraction carefully and consider leaving it switched on), and isolate the device from mechanical vibration (also consider fixing heavy components with silicone adhesive).