You might say we brag about things we have that are good that others don't have. But last night I suddenly realized that we actually don't brag about things we have, subjectively. When we brag about something, we subjectively can't believe that we actually have it. 

We don't brag about things that are everyday to us no matter how great they might be perceived to other people. Why? Because we find them so mundane and matter of fact that we feel no need to brag. We 'have' them so intimately that our conscious mind doesn't waste energy thinking about us 'having' it. Subjectively we know we have it.

But when we don't feel like we have something. When it feels like we've caught lightning in a bottle. When our shadow, our subconscious, tells us: yes you are holding this thing... but you actually don't have it, rather it has you.... that's when we brag.