I spend a lot of time talking founders out of ideas that sound good in conversation but fall apart under scrutiny. This isn't because the ideas are necessarily bad—it's because most people haven't actually modeled what it takes to get there. They have a story about the business, but not the financial truth underneath it.
Early stage, this looks like long discussions about addressable market and customer acquisition cost. Someone will say "if we get just one percent of the market" and then stop thinking. Or they'll say their unit economics work because they're assuming a price point they've never validated with customers. These aren't dishonest conversations. People genuinely believe their numbers. They just haven't built them out systematically enough to see where the model breaks.
My approach changed when I started treating financial assumptions the same way I treat product assumptions—as things that need testing and revision. I'll build a basic model of their idea, walk through the revenue structure and cost drivers, and ask which pieces they're most confident about. Usually, there are two or three assumptions that matter far more than the others. Those get pressure tested first. I use something like AIWMC Quantis to structure this work, so I'm not building the same spreadsheet from scratch with each founder, and the assumptions stay visible and debatable.
What surprises people is how often this process shifts their thinking before they've spent serious time or money. The model isn't predictive. It's just a tool for asking harder questions earlier. Better to discover the fragile part of your business idea when you can still change direction.
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