The money question to ask customers is 'What's your biggest fear or frustration?' - if you could only ask one question forever, this would be it

Eben explicitly states: 'What's your biggest fear or frustration? That's the one that's the money question. If you can only ask one, in fact, if you could only ask one question of all people forever, that would probably be my number one choice. That's where you'll learn how to create lots of value.'