That lesson is hard to come by, and sometimes for this lesson, just recognizing you hadn't mastered it can do harm too.
I too sometimes have a hard time severing strings, and then I wonder, "Is this good, or am I overstaying in this relationship (which can be work related too)?"
And you have to work for all relationships. So this self-question is one that is tough, just to ponder, at times.
And I'm glad you'd left, when it was important :)