It’s often easy to shoot down a moonshot idea that another person presents you with.
If he or she is your spouse, business partner or colleague, you know this person or at least, you think you do. Even though to you, the idea might seem so outlandish that it might not happen, don’t shoot it down.
Your duty is not to criticize the idea and tell him or her how it won’t work, no. You were approached because this person valued your input. And if you had nothing to say or do about it, just keep quiet.