First, let's introduce an evolutionary mechanism called the Reward System (not sure how it's translated into English, but the idea is there). For example, the man (back in those long long ago years) who just ran away from the wild beast (hello to modern sports!). He's elated. From the evolutionary point of view he did well, so he gets a reward - that's where the brain chemistry part appears on the scene.
Endorphins, serotonins, oxytocins and/or other hormones are "injected" into the bloodstream. I've read that even when your post is liked, say, on Facebook, your oxytocin levels are on the rise. Just like from getting and giving the hugs. The sex drive that is oh so strong - the propagation of the population and hence the reward (no need to expound on that). The man has eaten his fill (rare occasion in those scanty-ration times) - again he feels elated. So many people getting overweight these days.
Thus people become (volens nolens) addicts - they try to "hack" the Reward System, abuse it in order to get another portion of their high. The whole civilisation hooked on this or that. Hence the addictions - alcohol, drugs, sex, melodramas, sitcoms, sports, news... (I used to be a sugar addict (cupcakes and their likes)). There's these self-deception and (self-)delusion games going on around (and within) all the time. To get high. Making excuses. Resorting to cunning tricks. The mind is playing the game of self-indulgence oh so well. Only if for just a little more.
When you tamper with the Reward System (or, more directly, with the Brain Chemistry) regularly, it happens so, that it readjusts itself to a new "norm", and you need more and more of that substance, stimulae etc.
Whereas simple things, like watching the sunset or sunrise, can have the same exhilarating effect on you. Go natural!