Problems occur if a change in the system state happens unnoticed (initiated by the system, or by another person, such as the user who was previously using the machine), or if after some time the user forgets about the state change. Another typical problem is a sudden change of state that interrupts a user's activity, such as focus stealing. In such a situation it can easily happen that the user does some operations with the old state in mind, while the brain has not yet fully processed the signals indicating the state change.