I often find myself painting in more than one color at a time and using more than one brush at a time. I always make the same mistake and end up not only mad at myself but spending time correcting a painting that could be better spent.
The picture below shows how I usually end up holding brushes without even thinking about it. I just naturally end up holding brushes this way when I'm in the zone and don't realize the error until the "oopsie" is made.
Multiple brush no-no |