It's the users' perception of the system that may ultimately determine whether it succeeds, and in certain situations, whether it even gets done. Many promising knowledge sharing systems, and intranets in general, end up failing because they were created without an explicit, business-process-targeted goal. It's difficult for employees to get excited about contributing to a system when wishy-washy and overly generic mandates such as "to improve corporate collaboration" or "to share information among departmental workgroups" are given.
In order to grab the interest of those who will be participating in the development of a knowledge sharing system, the mandate must target a specific, real-world problem that employees can relate to. By doing so, you're providing employees with direct context — a practical application for the knowledge sharing system.
This mentality is very similar to our motivation to learn something new when we were studying our trades in school. For example, it was often difficult to learn a new programming language simply for the sake of meeting the requirements of the curriculum. Cracking open that back-breaking textbook and reading chapter after chapter was an exercise in tedium. But when asked to write a program with a clearly defined goal, many students picked up the new language out of a practical need. We had a problem to solve and we were motivated to build something to solve that problem.