This is usually related to an event happening in childhood, but not necessarily. Using EFT, we address the issue on the person we were at that time, our "ECHO". We no longer are this person, but this person is still in us, and more specifically, we still carry what they learned at the time ("the teacher said I was not good enough, that must be true. I will never be good enough.").
It gives us a second chance to review the reaction we had at that time, and change it with the insight and wisdom we gained since the original event. While we don't change what happened at the time, we change our perception of it, and therefore, what would have been a traumatic memory can become a non-event.