Excerpts from REALITY IS BROKEN, by Jane McGonigal.

Fiero is the Italian word for “pride,” – (we don’t have a good word for in English)and it’s been adopted by game designers to describe an emotional high. Fiero is what we feel after we triumph over adversity. You know it when you feel it – and when you see it. That’s because we almost all express fiero in exactly the same way: we throw our arms over our head and yell.
… it’s a craving for challenges that we can overcome, battles we can win, and dangers we can vanquish. Scientists have documented that fiero is one of the most powerful neurochemical highs we can experience. It involves 3 different structures of the reward circuitry of the brain, including the mesocorticolimbic center, which is most typically associated with reward and addiction. It is a rush, unlike any other, and the more challenging the obstacle we overcome, the more intense the fiero.

When we try to find happiness outside of ourselves, we’re focused on what positive psychologists call “extrinsic” rewards – money, material goods, status, or praise. When we get what we want, we feel good. Unfortunately, the pleasures of found happiness don’t last very long. We build up a tolerance for our favourite things and start to want more. This process ‘hedonic adaptation,’- is one of the biggest hindrances to long-term life satisfaction.

On the other hand, when we set out to make our own happiness, we’re focused on activity that generates intrinsic rewards – the positive emotions, personal strengths, and social connections that we build by engaging intensely with the world around us. We’re not looking for praise or payouts. The very act of what we’re doing, the enjoyment of being fully engaged, is enough.
The scientific term for this kind of self-motivated, self-rewarding activity is autotelic (from the Greek words for ‘self,’ auto, and ‘goal, telos). We do autotelic work because it engages us completely, and because intense engagement is the most pleasurable, satisfying, and meaningful emotional state we can experience.

As de Botton writes, "Long before we ever earned any money, we were aware of the necessity of keeping busy: we knew the satisfaction of stacking bricks, pouring water into and out of containers and moving sand from one pit to another, untroubled by the greater purpose of our actions." In casual games, there is no greater purpose to our actions - we are simply enjoying our ability to make something happen.