alt Hacker NewsHumans are terrible at doing what's best for them. They are pretty good at following local gradients, though. Smoking might kill you in 30 years, but right now it lets you fit in with the cool kids, or feels good once you're hooked. Not brushing your teeth might be terrible for them and your gums, eventually, but right now it saves you from having to do something.
At any given decision point, people are more likely to pick the option that provides some benefit to them. That looks very different from consistently picking the choice that is eventually best for them.
One reasoning flaw I've seen in this type of discussion is the assumption that the person has the same value system as you / the experts. In your example, it is assumed that the subject values a very long life. Maybe they don't, maybe they value smoking way more than a long life.
I largely agree with you, but I would tweak it to say "Humans are decent at doing what's best for them given their own values and knowledge".