[j.p.s]

Originally Posted by Quoth

I've spun up drives unused for 25 years.
It's loads of on/off cycles that can cause failure to spin up.

There is also bearing lubrication loss, head(s) welding to platter, and humidity degrading electronics. An example of a drive spinning up and working after 25 years of storage is no indication that this is typical. Although it is likely rare, I have no doubt that there has been a drive that was used for backup out of the box, stored a few weeks, then powered on and promptly died from infant mortality.

Originally Posted by ownedbycats

There's also sudden catastrophes. My external drive had been fine until I accidentally bumped it while it was running. Head crash!

There are many ways for drives to die without warning (or time to address a warning). I was only addressing the concept of SMART as some kind of insurance policy.