Well you kind of led them down a path to failure/wasted effort. One of the best ways to prevent these kinds of unhappy conversational paths is pre-emption. If you've already considered A, B, and C, then you can assume that someone else might think of them, and you should mention them in your initial problem statement. "I tried A but then realized it wouldn't work because of B." Now you've communicated the same information and skipped the part where you ask them for ideas and instantly reject them. They may still be equally unable to offer a solution, but at least they haven't gotten frustrated and given up before understanding the true problem.