Perhaps the ego gets in the way.

We're just not properly equipped to interpret our own cues because we're not used to looking at ourselves from the outside. An equivalent situation: I don't like listening to recordings of my own voice, because I'm hearing it without the resonance provided by my own skull, sinuses and auditory systems - it's flat and devoid of what I perceive as making it unique to me. Others, however, are used to listening to me that way. My self-image has more to do with what I see when I look down at myself (meaning from the sternum down and not including my back) than with what I see in photos or the mirror. Those are alien viewpoints.

I think the separation between mind and body so prevalent in our culture likely plays a part in it.

I believe that self-deception is a key factor in helping us get through, just get through. We repress what we can't deal with, and we tell ourselves all kinds of things that our purely rational selves would never believe.

One universal example (and I sometimes have to lean on this too): There IS life (as we think we know it) after death; we WILL see the loved ones we have lost again.

It's hard to continue without that one, I think.

Or perhaps the conclusion is false. People use video of themselves to improve everything from speech pattern to golf swings. Subjective judgment, on the other hand, by other people is just that, subjective. You could just as well write a horoscope and many people will agree that it's true about a given character (yeah, he's a Virgo, easy).