If a man is hungry, you can give him a fish. Better still, you can teach him to fish. Better still, you can teach him to invent a way to fish - Sean Hanly.
Extreme Programming forces the business to come down to the developers' level. Scrum forces the developers to come up to the business level.
Focus your customer on results not methods.
You want repeatable results not repeatable process - Sean Hanly.
If it was your money would you spend it on writing a PRD? If it was my money I'd want to see working software - Kent Beck.
Self-organisation pushes decisions down and out.
Have the customer define the budget. And let the team own it.
Sean Hanly talked about Shu Ha Ri as the phases of learning reflected in the adoption of agile methods.
Shu: Dogmatically follow the techniques to learn their intricacies and understand how and why they work.
Ha: Break away, using your expertise in the techniques to adapt them and learn their limits in different situations.
Ri: Achieve fluency with adapted techniques.
I liked Todd Little's analogy for planning with uncertainty using Hurricane Rita's projected path. You couldn't predict where Hurricane Rita would eventually hit the south coast of the US but you could manage for the uncertainty.