Ries wants you to stop guessing. Instead of spending two years building something nobody asked for, you ship the smallest version that tests the one thing you are least sure about, watch what people actually do with it, and change course from there. Build, measure, learn, then do it again.
The writing repeats itself and leans hard on its own vocabulary. The idea underneath is now simply how good teams work, which is the best thing you can say about a business book. Most products that fail did not fail at the building. They failed at checking whether anyone wanted the thing.