We men don't think of ourselves as moody. Except maybe if our favorite sports team makes a nonsensical trade, and it feels like a personal betrayal. But of course we have more moods than that. And those moods—such as being mad, frustrated, nervous, or even ecstatic—can alter more than your mind. They can affect your muscles.
What you're feeling can make you put less into your workout, or cause you to skip it altogether. But those same moods can be used to help your lifting session.