There's a lot more at work here that makes this posture so powerful.
We've seen that when we focus on what we have going for us, we fortify our confidence and raise our spirits. We enliven ourselves. In contrast, a deficit orientation can be deadening. Even more, it often leads to fear and defensiveness, two of the greatest inhibitors to human enterprise.
That sure fits with my own experience. I know that when I'm feeling threatened, I want to hunker down and shut out the world. And when I feel good about myself--capable and competent, supported and fortified--I'm much more likely to be open-minded, try new things, even take initiative. Probably you've had similar experiences.
Research into brain chemistry has shown that these reactions happen at a cellular level, far outside our conscious control. It's widely known that anxiety and fear activate the most primitive parts of our brains, triggering the fight-or-flight response that shuts down rational thought processes. In fear mode, instinctive reactions are often all we can muster. After all, it's hard to be creative or thoughtful when your brain is busy fighting off a tiger.
When we feel more secure, we activate the parts of our brains responsible for logical thinking. We become physically able to think more clearly. What's more, we're more likely to experience positive affect, which has been linked to increases in creativity, learning capacity (especially when learning something new), decision making and judgment, pro-social behavior, and emotional intelligence.
(We're also healthier in general: Positive connections with others have been shown to promote physical health. This is very important to me, as I've seen, and felt in myself, what we commonly call burnout, so prevalent among those most dedicated to the common good.)
When we pay attention to success and let ourselves feel good about what we've accomplished, we take full advantage of what's known about the way our brains work.