Love the comment here around YC interviewers changing their decision from default no to default yes

"If I had to decide whether to fund startups based on a single question, it would be "How do you know people want this?"

The most convincing answer is "Because we and our friends want it." It's even better when this is followed by the news that you've already built a prototype, and even though it's very crude, your friends are using it, and it's spreading by word of mouth. If you can say that and you're not lying, the partners will switch from default no to default yes. Meaning you're in unless there's some other disqualifying flaw."

How to craft a compelling product vision - using ARRO as an example with visuals etc