Your mileage may vary with this tactic, but for years we've found that if we introduce the idea of something and ask for an immediate decision, we will often get resistance and "no" for an answer. If we introduce the idea, maybe briefly discuss it, but don't ask for (or even hint that we want) an answer - often our DD15 will come around to the idea after she has had time to mull it over. Sometimes we'll even bring something up right before we have to go somewhere or do something else, so "oops, let's finish talking about this later." Then, a couple of days later when it is brought up, DD is suddenly much more open to it. Other times we'll start the conversation with "You don't have to make a decision now, but have you thought about..."
I don't know if it is a fear of change that causes the quick rejection? Or if the bad aspects/worst case scenarios are the first to come to mind? Maybe it is related to perfectionism, and our DD says "no" because she is not already an expert at whatever it is? For some reason, bringing it up, pausing, and revisiting it later yields a much higher number of "yes" answers.
Best of luck,
--S.F.
