No matter how good you are or how perfect you may be, it will happen eventually. You will make a mistake. Realize that you are human and know that even if you look something over multiple times, errors will creep in.
Reviewing material compiled years ago may cause you to notice errors as well.
And a big "thank you" to a regular reader who very graciously lets me know when a typo has crept into a blog post here. The notice and the way they go about it is greatly appreciated!