Telling a friend privately that their idea won’t work is more loyal than clapping for it publicly.

Applause is the cheaper support and it feels like the warmer one. Clapping for something you think will fail protects the mood and leaves your friend walking into the wall alone. Saying it quietly costs you ten uncomfortable minutes and gives them a chance to change course.

Say it one to one, early, and attach the specific worry rather than a verdict: the money, the timing, the part that depends on somebody else. Then ask what they want to do and back that. Nobody hears criticism well with an audience, which is why the private version is the loyal one.