(Things aren't always what they seem, and the same goes for people.)
It's a commonly held belief, a theory by many supposed, that inside every fat person a thin person's enclosed.
And it's often been said before (though that doesn't make it less truth) that inside many a middle-aged man beats the heart of a passionate youth.
A girl who appears just a butterfly may deep down be a slave to her duty; and one with the plainest exterior may be blessed with a soul full of beauty.
But here is another hypothesis I'd respectfully like to suggest - if no-one has any objection - that might take up its place with the rest.
If I'd courage to match my conviction I might stand on the table and shout, but it's this. . . . Inside every introvert there's an extrovert trying to get out.