Be frightened/nervous/scared of your own shadow British American phrase hyperbole
Be easily frightened ; be very nervous, timid, and afraid
I don't have much faith in David winning this competition because he's scared of his own shadow.
Since the attack she's nervous about her own shadow, and she doesn't come home late at night anymore.
Hey! You must stop being frightened about your own shadow and be confident. This task is just a piece of cake, and you can do it well.
This hyperbole has been used since the early 1500s in English, and some authors think it originated in ancient Greece.
someone believe that they are allowed to do whatever they want in their own home
It is always advised that wherever you go, a man's home is his castle