Researcher Robert Sapolsky has nailed it. We are dopamine junkies...
Those of us who are flops in life can't handle time delay of more than a day or week. But as Sapolsky points out, the typical successful middle class dopamine junkie can hold out for the reward of "getting into the best nursing home". The truly long distance and heroic dopamine junkies are the ones who can delay gratification into the hereafter, waiting for the reward that Saint Peter offers them.
Who says that reductive science can't take the measure of man? This talk is an excellent example of reducing a human to a single neurochemical.
If you are dopamine-driven and still haven't had enough Sapolsky, click here, here, here. And repeat that for 100,000 times!