Now, what I have is based upon my own experience, your mileage may vary and all that.
The players are running the party, so it goes on up the line in lessons learned.
I've seen truly stupid maneuvers from people in games. Things like charging at a foe who is obviously more powerful then the PCs, not scouting out an area before attacking, deliberately pissing off NPCs in positions of power, boldly ignoring warning signs of danger ahead, attacking when vastly outnumbered, the list goes on. I admit that I punish nonthinking players, stupidity kills in my games. I also reward problem solving, and I don't mean the "I kill it - problem solved" kind. If players only try to deal with encounters by killing whatever it is they just met, I let them achieve a TPK when they have met something tougher then they are. Attacking is only one option in a game, there are many more. If you cannot slay that dragon, why not try negotiation? If you cannot kill every orc in an oncoming army, use trickery and guile to fool them into not attacking? If the evil necromancer lich-king is too powerful for you, why not go out and gather allies together untill you have a fighting force capable of taking it out instead of doing a suicide charge?
Brains work just as adequitely as brawn in encounters. Just my own two cents worth.