Is there such a thing as healthy regret?

Keller, in a sermon entitled "Love Beyond Degree", says the following:

"There's things that have happened to us, and we have scars, and they're bad, and they still hurt, and yet the insight or the character or the strength that we've gotten from it, we wouldn't trade for anything."

I think that's a good definition of healthy regret. Imagine losing a child. You'll feel that loss as long as you're alive, even if that loss leads to wonderful things... Perhaps a deeper relationship with God. Perhaps a closer bond with your family. Perhaps a deeper appreciation for every day you have with the people you love. But an appreciation of the good that has come out of a loss doesn't mitigate the grief that's associated with its memory.

Similarly, when you think back to a time you've wronged someone you really care about, you feel the regret of having caused that person sorrow. Oftentimes, the remorse you feel for what you've done (and the resulting consequences of that action on the person you love) is an impetus to change the way you live your life. I think that's the rationale behind what Keller is saying, that you wouldn't want to change what happened for anything, even if at first you couldn't have believed that something positive would come of your suffering.