If you don't travel now, you might 'live to regret it'. [=you might feel sorry or disappointed about it in the future]
We 'regret' to inform you [=we are sorry to tell you] that we have offered the job to someone else.
It is to be 'regretted' [=it is regrettable/unfortunate] that the program has lost its funding.
(..) And you said never to use memories. I know I did. You're trying to keep her alive. You can't let her go. You don't understand. These are moments I regret. They're memories that I have to change. Well, what's down there that you regret? Listen, there's only one thing you need to understand about me. (..)2010 Inception
(..) - How do I know you can deliver? - You don't. But I can. So do you want to take a leap of faith... ...or become an old man, filled with regret... ...waiting to die alone? Assemble your team, Mr. Cobb. And choose your people more wisely. Look, I know how much you wanna go home. (..)2010 Inception