Wherever it comes from, it looks like it rests on an error, and a pernicious one. I will readily agree that people sometimes need to overcome their guilt. But, if it's true that you shouldn't feel guilty, then there is nothing to forgive. You don't need to be forgiven, you need to adjust your views. Similarly, people often need to learn not to feel shame about certain things. But, shame isn't overcome by forgiveness. It's overcome by changing what one thinks is worthy of shame. (And, there are things worthy of shame, just not a lot of the ones we grow up believing to be shameful.)
Forgiveness is something that can only be given by the person whom we have offended. And, it must be asked—begged—of them.
There is something strange about saying that I have offended myself. How would I give offense to myself? There are times when I may have hurt myself, but even there the notion of self-forgiveness is mistaken. Or so it seems to me.
Forgiveness is a two-person relation and necessarily non-reflexive. It is also a relation tied to other relations I cannot bear to myself. If I've harmed myself, I need to resolve not to do it again, but I can't forgive myself just as I cannot carry out any kind of reparation to myself, simply because I am one person and not two. How would I beg forgiveness of myself? How would I apologize? How would I make it up to myself? What reparation to myself would I propose?
Even so, I'm not so worried about people concerned about forgiving themselves when they have harmed themselves. This is because what people often mean in forgiving themselves is forgiving themselves for the offense they have given to others. As long as I can forgive myself, they think, it doesn't matter that I don't make it up to those I have offended. It doesn't matter that I don't apologize, that I don't have their forgiveness. All that really matters is that I have forgiven myself.
I am able, they say, to absolve myself of all my faults. And, thus do even justified guilt and shame disappear. Because, at the end of the day, all that matters is that I can live with myself.
There's as much narcissism here as in attempting to be one's own (best) friend.