The most useful thing anyone told me about my startup idea was the thing I didn't want to hear

My last product failed. 8 months building. Zero paying users.

The uncomfortable truth: I never let anyone actually challenge the idea. Friends said it was great. AI tools agreed with everything. I confused encouragement with validation.

Started over. This time I wanted the opposite — something that would tell me what the market actually shows, not what sounds good.

The thing I've noticed after talking to a lot of founders: the ones who caught their mistake early almost always had someone in their corner who was willing to say the uncomfortable thing at the right moment.

Most of us don't have that person.

How did you get honest feedback on your idea before you built it? What actually worked?