I am looking for a specific word that describes how someone would continuously do something that they think is good for themselves, but is really the opposite. What I mean by that is: whenever you do something that you think is good, but it actually harms you. For instance, people who drink diet sodas; they THINK it's good for them, but it's really not. However, they continue to do it. In simple words, it is whenever someone thinks what they are doing benefits them, but it doesn't. Help?
To answer livresque, it's a word that described someone; an adjective. "My friend is a(n) [unknown word] because he wants to drink diet soda, but he doesn't know it's bad for him."
To answer DjinTonic, it's not quite misinformed, though it could be. It was a very philosophical term one of my teachers briefly explained to me, but I just can't remember what it was. Without trying to be condescending, I doubt anyone here will guess it, I'm asking for a very specific term, one that not many people have heard.
To answer HippoSawrUs, I'm thinking about this in the context of a complex topic, much more complex than diet sodas (I just used the analogy to simplify it). I can be about a topic that affects a large group of people. For instance, let's take the United States economy vs environment debate: Should the US focus more on its economy or more on its environment? Most people would argue for the latter, but they don't necessarily know the impacts that it would bring upon them. I guess that's what I'm trying to get at, people choose to follow or do something that they think (or sounds) good for them, but they are oblivious to the consequences. And before you say it, no, the word I'm looking for is not obliviousness.
To answer Old Brixtonian, it's not used as an insult much. Although obstinate is on the right path. I'll do more research surrounding that word.
To answer Xanne: refer to people in cults as a more serious example. They think their way is best, and they think their way is right, but in reality, well, you can answer that question.
To answer Elliot: technically, yes, but that is not the word I'm looking for. The definition I provided does not fit the exact definition of disagree, nor does it fall in those lines.