It wouldn't kill you guys to explain why. If you tell someone that their idea won't work, then they will just have to keep coming back to you, asking if their next idea will work, and the idea after that, and after that. If you explain why, they can figure out if their next idea will work on their own, rather than having to come back to you. You know the old saying "Give a man a fish, feed him for today. Teach a man to fish, feed him for a lifetime" ?
Yes yes, he could search. However, I'm not finding THAT many threads on this subject that have anything useful/applicable in them. A sampling: