It's not too hard to sell someone on agile, whether internally or between organisations. Almost every objection from a traditional project perspective can be countered by the flexible change process, and the potential for better results, and ultimately lower costs. However, at best this creates passive acceptance, which is just about enough for someone not directly involved in a project, but can cause a project to become massively unstuck if that person is a dependency. It is also a fragile acceptance - if a project goes awry, then the merely accepting person is likely to start pushing back towards traditional methods, to the detriment of the project. The eventual failure then reinforces any existing reservations towards agile.

What agile needs to succeed in is understanding and support, and that requires a difficult mental shift - viewing work in terms of business value. Even experienced agile practitioners can get bogged down in implementation, and forget the why of what they are doing. This is because our experience teaches us to think in terms of problems and solutions, and to prefer the better known to the unfamiliar. We get so focused on building software we don't stop to think whether it does what we really need. Ryan Shriver describes this as not knowing the difference between "delivering things right, and delivering the right thing".