Mostly likely time a hard drive will fail?

1. When booting the drive.
2. During operation - none/minimal activity
3. During operation - heavy activity
4. When moving/physically handling the drive
5. When newly bought - first time booting
6. Other?

I have an old Quatum Fireball EX6.4A hard drive been using for about 10 years so far and it still seems to run just like the first day of use, even after years and years and countless hours of heavy workloads it still manages to keep on chugging. Incredible, I say.