How to prolong the life of an external hard drive?

If you put an external harddrive next to the server/desktop and:

• Do not carry it around in your bag like it is a piece of rock.
• Do not toss it around like a piece of fruit.
• Do not expose it to cold wet outside weather followed by dry hot (room) temperatures
• Do not unplug it and pick it up while it still is spinning.
• And mount it in a proper case with a decent PSU and sufficient cooling,
• ...

then I see no reason why they should not last just as long as internal drives.

Ofc, there is a reason why people buy external drives. And they often do get exposed to one or more of the conditions I mentioned above.

The primary reason I've come across for external hard drives dieing earlier is due to insufficient cooling in the enclosure; heat will kill a drive if allowed to.