The idea that the problem with giving up is determined by which drug it is, in a way that is consistent across all users, never seems convincing to me.

That's especially the case for tobacco. Clearly for many people it's desperately hard to give up, virtually impossible even. For others it's no problem at all even after years of smoking. I was fortunate in that I never had any problem. Just decided to stop, and stopped.

I don't think it's a matter of willpower, but rather of the way our body chemistry works. There may well be other types of addiction for which my experience would be the reverse.

And the reason I think that matters is because generalisations about how addictive or non-addictive various drugs are - ranging from caffeine to heroin - are liable to have effects. We hear from friends about how desperately hard it is to give up smoking, and we believe that will apply to us, and that in itself can make it harder than it really should be. Or it might go the other way - friends find it easy to give up some recreational substance, and we assume that will apply to us as well, and maybe in our case we will find it desperately hard