Revolutionary Products, Existing Demand
Your product can be the newest, coolest thing around, but it still needs to serve existing demand in the market. Even the iPad was introduced by listing the activities people already do that it improved upon:
Web browsing
Email
Photo management
Watching video
Listening to music
Playing games
Reading eBooks
By itself, the list borders on mundane.
Ash Maurya, a leader in the Lean Startup community, made this great point on the latest episode of the Jobs-to-be-Done podcast. Check that out for more.
