For Peat's Sake and The Threat of Flame are a pair of quests in Wetlands, and a perfect example of Being Too Helpful.
For Peat's Sake you put out fires using a magical enchanted blessed lily blossom which sprays water. And the quest giver gives some helpful advice.
"The blossom may also prove useful against the elementals themselves."
And in fact using it near them will cause them to become doused. I don't actually know if this makes them hit softer or have less health, but they do look smaller, so that must mean something good.
Except Doused Fire Elementals are not part of the quest objective. That's right, if you follow the NPC's advice, you will not be able to complete the other quest, because his advice changes them into a mob that doesn't give credit.
And that, is Being Too Helpful.