Two of the most common reasons for failing to achieve critical mass are lack of interoperability and the lack of appropriate individual benefit. Compatibility issues lead to general wariness among customers, who want to wait until a clear standard has emerged. Even when everyone in the group may benefit, if the choice is made by individuals, the system may not succeed. However, if it's not easy to enter your appointments, then it may be perceived by users as more beneficial to leave their own appointments off, while viewing other people's appointments. This disparity of individual and group benefit is discussed in game theory as the prisoner's dilemma or the commons problem.
Most people are familiar with the problem of spamming with email.
However, individuals have the incentive to graze as many cattle as possible on the commons as opposed to their own private property. If too many people send too many cattle to the commons, the area will be destroyed, and the whole village is worse off as a result. These solutions are an appropriate starting point for solving problems of abuse in groupware. When someone asks a question, they usually expect either an answer or a request for clarification. After a request, a typical response is to fulfill the request or specify a reason for not fulfilling the request.