When I heard of FOCUS for the first time I was a bit skeptical as I was not sure that it is possible to create a one-size-fits-all workbook for startups. And FOCUS sounded to me exactly like that. Luckily, it isn’t: instead through a series of exercises and tasks Justin lays out one of the most universal principles in solving problems: first you brainstorm on your idea and hypothesis, then you test it in real world, collect data in a systematic way from the real people/customers and decide how to move on based on facts, not on beliefs.