We have the ability to envision (simulate) future happiness. We tend to think that external events or things will cause us to be happy or unhappy because that is what our culture teaches us. In our capitalistic consumer-driven world we are bombarded with messages telling us more is better and that things can make us happy. We would be happy if only we had that car, or that computer, that house, that vacation, those clothes - ad infinitum.
We are tricked/indoctrinated/brainwashed into this way of thinking because that is what drives our economy. Very little could be marketed to the Zen Buddhists or followers of the teachings of Jesus, - because they don't want "things", consequently we see Zen ideas relegated to fringe groups, and mainstream pseudo-Christian teachings that fit in both with capitalism and the associated idea that external things bring happiness - peace, love, and joy.
The fact of the matter is that we make our own happiness and it has very little to do with external events. We all have some idea about how this works when we see people who supposedly "have it all" but turn out to be miserable and others who have very "have very little" - and yet are quite happy.
One of the counterintuitive examples Dan Gilbert uses is our ability to predict what impact two extremely different events would have on our lives. Losing the use of our legs and winning the lottery. You'd think one would clearly make us unhappy and the other happy - turns out that 's not the case. Research showed that six months after those events occurred people were just as happy (or unhappy) as they were prior.
Happiness comes from the inside-out not from the outside-in. It doesn't matter where you are, who you are, what you do - you have the ability to choose your attitude - including an attitude of happiness. Not to say that's easy, but if we could give up on the idea that happiness is something that lies in the future after we get that car, job, house, wife, husband, etc..etc..etc.. we would at least have a fighting chance of finding peace, love and joy (happiness) right here right now.
This video of Dan Gilbert's presenting some of his ideas, is one of many interesting pieces available from Technology Entertainment Design (TED)