In the spirit of such threads as:
Unpopular opinions you have
You Know What Really Grinds My Gears...
and
You Know What Really Makes Me Happy...
Verb
Feel sad, repentant, or disappointed over (something that has happened or been done, esp. a loss or missed opportunity).
Noun
A feeling of sadness, repentance, or disappointment over something that has happened or been done.
Synonyms
verb. rue - deplore - repent - lament - mourn - be sorry
noun. repentance - remorse - sorrow - grief - contrition
What are your regrets?
It could be something simple, like not getting that double-double this morning. Or something more deep, like not taking that career opportunity when it came up.
I'll start:
I regret not taking my laptop home with me last week. So now I'm 3 days behind on work because of being stuck at home with this strep throat.