Product-market fit is when a product is a good match for the market. That means that people in the market really like the product and want to buy it.
To determine if a product is a good match for its intended market, businesses use a guideline known as the 40% rule. This rule suggests that for a product to achieve product-market fit, at least 40% of the users should indicate they would be "very disappointed" if they could no longer use the product.
When users say they would be "very disappointed" if they couldn't use the product anymore, it indicates a high level of satisfaction and reliance on the product. These users are more likely to continue using the product, and they are also more likely to recommend it to others. In this way, having a high percentage of users who say they would be "very disappointed" is a strong indicator of a product's success and potential growth in the market.