After enough crying, screaming or rage the parent or someone else gave them something to distract, satisfy and shut them up. I recently saw a small child bumped accidentally by an adult. The child was surprised and when the adult leaned down to apologize, he started to cry. Then he realized he was supposed to be unhappy and cry. We unquestioningly accept that unhappiness is our normal emotional state - We assume happiness lies outside of our normal state.
Happiness is equated with getting, acquiring or accomplishing something.
For example, remember the American Express commercial where a flight is canceled and a man is trying to get home for his daughter's school play. He whips out his AmEx card and buys a first class ticket on another airline. He has no cash for a cab and the line is long so he gets a AmEx cash advance and rents a limo to get to school just in time.