Sure you're beautiful, but...
This is another beautiful quote by Rumi. That said, I see much more than beauty in others. I see disgust, joy, stupidity, lust, shame and the list goes on for good and otherwise. Rumi didn't only mention beauty to be nice to us here, he was addressing multiple things.
First, and most obvious, he was addressing that what we see is what we are. Everything we see is what we are, not just beauty.
But the other aspect of this is his experience of others seeing beauty through him. We could assume Rumi had a very high level of self-love, so high in fact that others could only see beauty in his presence.
Two people that experience a moment, have completely independent experiences. Each individual is reflecting and experiencing themself through the other. We will naturally experience less conflict with others when we have less active conflicts with ourselves.
Rumi is not saying that you are beautiful, of course, you are, but you are not only beautiful. You are everything you experience, and that is the depth of the beauty you possess.
I love you,