I'd be careful with people shutting down my ideas up front, in casual conversation.
Sure, you may end up discarding your ideas yourself, but if you instead sought to implement them you could learn something in the way, maybe turn them into something that would actually make sense. That would not happen if you just followed advice from some authority and simply decided not to experiment with your ideas any further. So I'd not discard advice from knowledgeable people, but I would not take it as a final word either.
Sure, you may end up discarding your ideas yourself, but if you instead sought to implement them you could learn something in the way, maybe turn them into something that would actually make sense. That would not happen if you just followed advice from some authority and simply decided not to experiment with your ideas any further. So I'd not discard advice from knowledgeable people, but I would not take it as a final word either.