"Sure, but that's objectively true," I replied, "You're a Doppelgänger."
"Yeah, but a real Doppelgänger would respond to that feeling by being sneakier and more devious, rather than experiencing further doubt. It's like the Doppelgänger saying goes: work more insidiously, not harder."
"Is it possible that, instead of a failure on your part, other Doppelgängers are undermining you with subtle cues, and you're internalizing that doubt because it's too perilous to confront their subtly rude behavior?"
"Oh, hey, that reminds me, I need to learn to cast micro-aggression without verbal components so I can crush their minds to powder a tiny comment at a time!" she replied, "That'll probably help with this latest thing too."
My friend is very dedicated to her job! And also to subverting and destroying her job! This may be paradoxical to you, but if so, maybe you're not a very good Doppelgänger.