It's better to regret something you HAVE done

this is ometimes quoted as an Orbital lyric. Much as I like Orbital, this is not an Orbital lyric as such. They sampled it for their track Satan from The Butthole surfers.

The original goes like this (in a cheezy American accent with quiet strings in the background.)

With things left undone we are left with only the mistake and the missed opportunity, frequently there is no way to go back and try again.

Many adults (older than the age of 20) speak about regret much more than "youthful mistakes." This is why most older people encourage youth to gather ye rosebuds while ye may.

old Irish saying:

"I have done the things I should not have done,
I have left undone the things I should have done,
and there is no good in me."

We have left undone those things which we ought to have done;
And we have done those things which we ought not to have done;
And there is no health in us.