Beliefs have their own shadows, and beliefs also create identities with their own (very similar) shadows.
The shadow of a belief is all the reversals of the thought or idea believed in. The shadow of an identity is anything that does not fit into the identity. And any belief creates an identity.
Say I have the thought that people shouldn't lie, and believe in it.
The shadow of the belief is the grain of truth in each of its turnarounds, mainly that people should lie. Why should they? Because they do. And because people often have good reasons for it, at least as it appears to themselves. There are many reasons why people should lie, and even the gifts in it, and I can always find one more.
The shadow of the identity is the ways I lie. My identity is as someone who does not lie, so the shadow is the ways I lie in my own life. How do I lie? At one level, everything I say is a lie, or rather at best only a relative and limited truth. At another, more conventional level, I lie as well. I may come up against a threat to an identity, and come up with an (apparently innocent) lie to protect it. And I also lie to myself in many ways. I lie to myself when I believe in any thought, since I at another level already know it is not true. The list is endless, and here too, I can always come up with yet another example.
The shadow of the belief has to do with how I box the world in, and the shadow of the identity has to do with how I box myself in. And the two are of course closely related, just two faces of the same boxing in.