Why is a perfect friendship the exception rather than the rule?
I would say it’s not even the exception, simply a fantasy. Real people in real relationships run into real problems if the relationship lasts more than a short period. That’s not an imperfection, that’s just life doing it’s job — providing us with challenges so we can grow and develop. So you could say that ALL relationships are perfect in that sense — they’re producing the exact problems we need at the time to learn our next lessons. The only imperfection here would be holding on to some fixed ideal of the perfect relationship, and believing that there’s something wrong because you don’t have that.