“Sean Ellis developed a simple test: if you were no longer able to use this product today, how disappointed would you be — very disappointed, somewhat, or not? The golden benchmark is 40%. Like Superhuman did, you can segment that data to find the nucleus of your highest-intent users and use it to build a product roadmap that moves you over the line.”

Use the 40% disappointment test to quantify product-market fit — not just 'feel it when you see it'

The binary 'you'll know it when you see it' PMF definition is not actionable. The 40% threshold gives a directional score that can be tracked over time and segmented by user type. Superhuman ran this test iteratively — found they were below 40%, identified which segments were closest, talked to those users, built toward their needs, and systematically crossed the threshold.