Here are two queuing behaviors that enormously complicate the type of closed-form analysis you have just completed (the homework problem for chapter 2). Indeed, the closed-form analyses become unworkable, so we must use simulation! Here are the 2 behaviors:

1) Balking: The entity (e.g., a person) comes to the queue and thinks "It's too long. I refuse to join it."

2) Reneging: The entity joins the queue, it moves very slowly, and the entity (e.g., a person) decides "Never mind. I'm going home" and leaves the queue before receiving service.

So, by definition, a balking entity spends time = 0 in the queue. A reneging entity spends time > 0 in the queue.

Soon we will look at how simulation can model such behavior in a system. When have you balked or reneged?