XP is ideally suited to projects requiring the close cooperation of specialists. One challenge at the beginning of such projects is getting everyone to work in concert while learning a bit about each others' specialities. For example, once I worked on a life insurance project. The actuary was patient with me as I began to learn enough actuarial math to pair with him. After a month, I was catching stupid mistakes. After several months, I was even helpful sometimes. I never became an actuary, but the resulting system (and team) was much stronger than if the actuary worked on his little corner of the system while I worked alone on the user interface.