regret
/ri-ˈgret/
verb
to mourn the loss or death of
to miss very much
to be very sorry for
noun
sorrow aroused by circumstances beyond one's control or power to repair
an expression of distressing emotion (such as sorrow)
a note politely declining an invitation
idiom
to feel sorry or disappointed about (something) in the future
If you don't travel now, you might live to regret it.