“The only way to know if it's a must-have is to get it in the hands of potential customers and ask them how they would feel if they could no longer use it. If they wouldn't care then your product's not a must-have.”

The "Very Disappointed" Survey Is the Only Reliable Must-Have Signal

Sean Ellis coined the PMF survey question used by hundreds of companies: if more than 40% of users say they'd be 'very disappointed' if the product disappeared, you have enough signal to build a growth engine. Below that, you're still iterating toward must-have. The threshold isn't magic — it's the minimum observed level where sustainable growth is consistently achievable.