Selfies help us confirm that we do indeed have a head... so do mirrors. Otherwise, we are headless - there is no way to truly see, except by inference.
Other people's affirmations that we do have a head are anecdotal, and we are happy to trust that. Left to our own devices we might be left with some reasonable doubt - the unconfirmed.
This gap is the key to why we are captivated by our reflected self-image in others... we see ourselves in others and we affirm what our eyes cannot ever witness directly. It's a dependency that leaves us vulnerable to market forces.
Mind the Gap.