EvolutionarySOA - Martin Fowler : "Evolutionary design is an essential aspect of agile methods. One of the key foundations of agile methods is the desire to handle, indeed welcome, change.
Planned design assumes change is hard, and thus tries to predict where it occurs.
If changes occur within the predicted boundaries then it's easy, but if it falls outside those boundaries you're out of luck.
Agile thinking assumes unpredictable change is inevitable and tries to enable it in a controlled way."