Perhaps it's because we know our faults, our weaknesses, our fears. So when others see the beauty in us the thought that comes to mind is "oh, but they don't really know me."
For me, it helps to think about all my blessings and focus on that, trying to remember the positives, accepting what others see in us.
Think about the wonderful-ness of you and know you have touched many.
I wish you peace.