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.
(..) Intoxicating, isn't it? Hi. What's going on? Here's the thing. "Just as Oppenheimer came to regret his contributions "to the first atomic bomb, "so too I regret my participation in what was, "at the very least, an error in judgment. (..)2007 TvShow: The Big Bang Theory Title: The Big Bran Hypothesis Season: 1 Episode 2