They’ll be your unwitting accomplice and provide the “validation” you’re looking for — leading you in the wrong direction. To the best of your abilities, avoid even thinking about your idea during the interview — and certainly avoid talking about it. These interviews are about your customers and their problems. Do your best to keep the conversation focused there.
Once your idea pops into your brain during an interview, your body will literally turn against you. It will start looking for validation that the idea is good. Your interpretations of statements, intonation, body language will all be skewed. What’s worse, the person you’re talking to subconsciously knows what you’re looking for, and based on our desire to build relationships, will want to help you.