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 forgot to mention "heat" which is a serious 6.

if there is no proper cooling the probability of a HDD failing is proportional to the temperature...the higher it is the more likely it will fail