Why is it that we desire things but don't always enjoy them when we get them? In this longish (but pleasant to read) article, an explanation based on neuroscience is offered. Desire and pleasure are separate chemical systems in the brain. Dopamine is linked with desire, while opioids and endocannabinoids correlate with pleasure. The dopamine system is "vast and powerful"; the pleasure system is "anatomically tiny, has a far more fragile structure and is harder to trigger."