This idiom means very timid and fearful. This hyperbole has been used in English since the early 1500s, and some writers believe it originated in ancient Greece.
Example 1: Richard constantly worries about security; he's afraid of his own shadow.
Example 2: After Tom was robbed, he was even afraid of his own shadow.
Example 3: I have never seen anyone so easily scared - she's afraid of her own shadow.
Example 4: Some political leaders immersed in corruption are accompanied by high security forces because they are even afraid of their own shadows.