In many cases, you might have been employed because a company does not have the necessary skills or knowledge. Both you and the client have a responsibility to ensure that a learning transfer takes place during the change cycle so that the benefits of the contract are maximized. Your goal is to make sure that the essential elements of your competencies remain in the business. There are three types of knowledge that the client should seek to retain once you have left:
Tacit: the skills and knowledge that are used naturally without any overt thought.
Explicit: the codified skills and knowledge that you bring to the business.
Relational: wisdom that emerges as a result of the social interaction between the client, consultant, ...