“Whether this person is a designer, product manager, programmer, writer, consultant, or whatever, he/she comes with (1) a set of skills and (2) some explicit knowledge of the area in which skills are to be deployed. The skills alone aren’t enough. Domain knowledge is also required. The more important that domain knowledge is, the less fungible the people are. That means you can’t divide them up into pieces, but it also means that you can’t easily replace them with other people when they leave.”