I was thinking about this about an hour or so ago! I am confused too. But I think what some others have said sounds correct, that maybe it's about us learning our own limits and boundaries, if we have a healthy inner world where we can trust ourselves to keep ourselves safe, then we can choose better, healthier more satisfying relationships in the future.
People won't respond to us like a therapist does but I believe there must be people out there who add something positive to our lives, we won't get everything we need from one or two people but we'll look to lots of people for different things, and we'll also add something to their lives in turn.
I hope this is the case.