Mistaking the uniform for the person wearing it.
The persona is not a lie you chose. It was engineered, early, for a job: secure approval, avoid conflict, keep a volatile house from tipping over. Jung took the word from the Latin for an actor's mask, and he was careful about it. The mask is not fake so much as a compromise, between what you are and what the room needed you to be.1
In some houses the job was bigger than approval. The kid who got good at reading a room before anyone spoke. The one who became capable because somebody had to be, and hyper-rational because feeling would have been one more thing nobody could handle. Family therapists have a word for a child drafted into an adult's role: parentification.2 Being the reliable one was not a personality. It was tactical camouflage, and it worked, which is exactly why it is still on. The child who built it did so in the sense Faultless ↗ means: the only tool available, used well.
The cost of over-identification arrives late. You mistake the uniform for the person wearing it, and for a couple of decades it is a good enough mistake: the uniform gets promoted, stays married, gets relied on. Then the quiet dread, usually on an ordinary day. You have spent years optimizing an interface, and you are not sure anyone, including you, has met the operator.