I dentity

We hardly notice how much health is a part of our identity. Whether consciously or not, we have a self image that is usually tied to the energy or attitude. We may see ourselves as "big, strong" or "funny, easy-going" or "happy" or whatever.
We will rarely use the words to describe ourselves. We use those words to describe others. It could be said that we prefer to let our actions and attitude speak for themselves; or maybe we are just in denial about how much what we can do defines the person we see in the mirror. -- And how much we like that person.

The idea only asserts itself in our minds when some sort of significant change comes into our lives.
A person may work for months to lose weight and suddenly cannot stop speaking about how much better they feel; how much more energy they have. If you listen closely, you'll hear the tone of their voice and be confused: The person seems to be trying to convince themselves of what they're saying.
As if they can't believe this wonderful change themselves.

What's happened to them -- by their own choice and actions -- has made them reevaluate the person they see in the mirror, and they are still getting used to the idea.

Now, imagine for a moment another person who did not choose to change; and the change did not make them stronger and more energetic. Some sort of injury has changed their lives.
There is nothing to brag about. The person has to reevaluate. But their own confusion makes them seem insincere. They are in denial, and the pretense of health is obvious in their tone of voice. If we are not so full of ourselves that we cannot hear it.

In both cases, the person is dealing with an identity change.