I have this famous saying about editing: If it's wrong yesterday it's still wrong today.
What does that mean? When you're editing a manuscript and you spot a mistake, but you're not certain you don't overlook it and keep going. You use a resource like Grammar Girl to confirm your suspicion about whether it is right or wrong. Why? Because if it's wrong, it's wrong, period. The infamous grammar police aren't going to write you a kind note that says:
I suspect that the mistake on page 10 was something you questioned and then overlooked, but you did know it was wrong, right? So we're giving you a pass.
All our best,
The real trick is to know it could be wrong. I once played that Who Wants to Be a Millionaire board game with my family. I almost always won. Why? Not because I was the queen of trivia by any stretch of the imagination. It was because I knew what I didn't know -- and I knew to "phone a friend" or whatever the gimmick was. In editing you don't have to know every grammar, usage or style rule. You just have to know when to look it up!