Etiquette is all human social behavior. If you're a hermit on a mountain, you don't have to worry about etiquette; if somebody comes up the mountain, then you've got a problem. It matters because we want to live in reasonably harmonious communities.

You do not have to do everything disagreeable that you have a right to do.

I make a distinction between manners and etiquette - manners as the principles, which are eternal and universal, etiquette as the particular rules which are arbitrary and different in different times, different situations, different cultures.

The mistake people keep making is that if they find a wonderful new tool, like email, they have to give up all others. They don't. You have simply added another very useful means to your communications repertoire.