It is good to develop the habit of being on time. When we grow older and have fixed times for davening and learning, we surely do not want to be late. We will ruin the quality of the mitzvah by being late, and we might not even get the mitzvah at all. A leader needs the patience to relate to each individual Jew. Rashi is teaching us a basic principle in human relationships.
People are different.
The other person does not necessarily think the same way that I think. He may not like the same things that I like. It begins with little things. Yehoshua Bin Nun was able to get along with everyone. Children . . .