In Catcher in the Rye, the narrator failed his school so he had to leave. Before leaving, he thought to say good-by to his history teacher. Then, he brought up his memory of playing football with his friends till very late night when a biology teacher asked them to go back to dorm and have dinner. Immediately after that, the narrator said,
If I get a chance to remember to that kind of stuff, I can get a good-by when I need one----at least, most of the time I can.
How is his memory of playing football with friends connected to his belief in saying good-by when leaving a place?