Rarely can expectations be quantified. As components of a system people also have expectations, they are not simply a moving part. So people need to get something from a system and can't simply be seen as contributing to it. And those needs differ from person to person. Yet these needs must be considered in system processes.
People bring their values to systems.
If the system conflicts in some way with a person's values they may not contribute as expected or, conversely, if the see the system they are a part of as contributing to a greater good and that is important to them, then they may contribute much more than expected. People are not interchangeable parts. In other words a system with human components must be able to withstand people taking different paths than what you expect them to. They may actually find a better way. Addressed this question last.