If you ever had to convince a client or a boss why Agile works, you know that it's not an easy task. Agile goes against many ideas that are considered axioms in the business world - like planning first and then keeping to that plan: "plan your work, then work your plan". If that is the case, these points from a talk by Martin Fowler and Neal Ford (ThoughtWorks) might help you.

In the Plan Driven approach, a project is successful if it goes according to plan, so in software development it depends on requirements stability, on having clear and fixed requirements. As you probably know, that is a luxury most software projects don't have, and a first approach would be to apply techniques like Change Management or Sign In Blood to contain the changes. Unfortunately that leads to unhappy clients and unusable software.

The Agile approach is to break the dependency on requirements stability and come up with a process that takes into account changes. It does that by using Adaptive Planning and Evolutionary Design.

Adaptive planning implies going through the project cycle many times, re-planning and re-adapting often.

Evolutionary design can be achieved with the help of practices like Self Testing Code, Continuous Integration, Refactoring and Simple Design.

If this made you curious, I highly recommend that you view the complete talk here: