What are some of the causes of Willy's mental journeys into the past?

Willy is an escapist. He doesn't like his reality, and he isn't happy in the present, so he mentally checks out and sees things the way he thinks they should be (or should have been). This goes for his job, his children, their activities, and his wife. Let's face it, Willy never had an affair because he needed the mistress. He simply needed to feel special..... in a way that wasn't real.