why not to put two spaces after a period

Typesetters will definitely hate you if you do. Explanation HERE.

And the article is right about the stubbornness of people who think it’s two spaces. As an editor it’s sometimes like talking to a brick wall, telling people to use only one space when they’re sure you are wrong.

However, the mistake isn’t as inexplicable as the author of the article thinks. I clearly remember being taught in high school, over and over again, to use two spaces after a period. I only shook the habit because I had a friend whose family was in the newspaper business, and he explained the proper way to do it.