In the 7th-grade math class I teach, when we discussed closed and open intervals I stumbled a bit when it came to talking about 0.99999... possibly being the edge of an open interval. I told the students that for technical reasons we can't say that, and 0.99999... = 1, but to explain why would be too hard. Job Currell found out why from his brother Isaac, and we talked about it in class, which was good, but I thought I'd better write up a handout to explain this weirdness. It's something I'd never heard of myself before I was in my 50's, when Professor Christopher Connell told me about it. That handout became this Substack article.