Quote Originally Posted by Soulforged
But do you consider those elements as the only possible for verifiyng stupidity in a given case? What about the results? Acting passionaly could end in some benefits, either personal or general. Acting from your emotions isn't always stupid, and it can be instinctive in some cases.
Well, they are the only ones I can think of, nothing else seems to make much sense. I am not saying that every decision needs to be given hours of consideration, especially casual decisions made in a non threatening setting (with friends), and even emotional decisions or out bursts (a declaration of love or anger) are not always stupid, unless you are trying to hide your emotions.

Quote Originally Posted by Soulforged
If something stupid is always a mistake, then what's that something? What defines that mistake as stupid?
That “something” could be anything done without considering the facts, history and most probable outcomes that results in a bad thing. One could argue that the “something” was a measured risk with an acceptable negative outcome given the slim possibility of an anticipated positive result (lottery). A mistake can generate a positive outcome and a stupid mistake can be acceptable in ones opinion, the phrase “it’s better to have loved and lost than to have never loved at all” comes to mind. I suppose that if someone learns from the mistake then they could rationalize the “stupid” away as a learning experience, but if they repeat the same mistake again the “stupid” comes back.

Quote Originally Posted by Soulforged
You also could see situations in wich there's absolutely no mistake and we could call that stupid, this is mostly verified in the phenomenum of the masses, people following a movement without thinking twice for example, but a good movement. That can't be considered a mistake. The same happens with a movement that is neither bad nor good.
What kind of movement are you thinking about? The only thing I can think of that would be emotional is a riot or something of that nature, any other gathering or organized movement would have some kind of time frame to gather ones composure and would eliminate the emotional reaction. Peer pressure from someone reacting emotionally may trigger an emotional response, but if that lead to a mistake (crime, humiliating yourself, a preventable accident, etc.) the response would have probably been a stupid one.

Quote Originally Posted by Soulforged
But if subject A -stupid- ignores information, then what does it means that he ignores information? Stupid has to be either a superlative of ignorant or another category related to ignorancy in some way, in my opinion.
I am still of the opinion that stupid and ignorant are different but I guess someone could be stupid for being ignorant of something. I can think of lots of examples of this but I think someone can be ignorant of something and not have it related to a mistake at all, what I am ignorant of could fill a library, but that doesn’t mean every mistake I make is because of my ignorance.

Quote Originally Posted by Soulforged
So you also agree that stupidity is not the road to happiness. Or perhaps happiness is not what the human looks for or should look for? For another discussion.
IMO Ignorance is every bit as blissful as enlightenment. Someone enjoying the bliss of ignorance is happy that they are enlightened about all the things they know while being oblivious to the things they don’t. What you don’t know can’t hurt you. Ignorance, bliss and enlightenment are all relative terms.