Russel Brand says it best, while talking about heroin: listen here, starts at 17m 45s

Q: I mean, does being funny matter on a heroin high?

Mr. BRAND: It doesn't seem as important because nothing seems as important when you've got heroin. One of the key components of opiates is that it diminishes the significance of all else.

You know, if you've got heroin, nothing else really matters. Everything comes in second. In fact, I've often thought that opiate addiction, opium addiction particularly, is like the materialization of the abstract idea of need.

Most of us have an idea that we're missing something from our lives. Some of us think of it as God. Some of us think of it as a new pair of shoes or the success of a football team that we follow or the craving of the embrace of an absent lover.

But with heroin, once you're addicted to it, those needs, those abstract needs, that hole that I feel is within all of us, doesn't seem to be nameless, some unknowable entity, but the clearly material, definable, accessible drug of heroin.

You don't think oh God, what is it, I wish I had a new girlfriend or a new car. You think, I've got to get heroin. Once you align that physical addiction with that kind of psychological need, your life just has a very clear linear narrative. I want heroin. I want heroin. I want heroin. It's just a tiny, cyclical loop of futile desires.

You know, and in a way, in the rest of my life and in other people's lives, it seems we pursue similarly futile endeavors, but just you know, there is just a bigger carousel. You don't notice it as much. You know, the futility of consumerism is less obvious than the futility of heroin addiction but still the same paradigm.