When you're a digital artist, one of the primary tools in your arsenal is the mask. Derived, literally, I'm told, from the practice of using masking tape to block off areas of your surface that you didn't want to get mark-making material on (so 20th century!). Basically the process involves front-loading a small amount of time and effort into creating an "out-of-bounds" area, outside of which nothing you do will be visible, so that you can be your fabulous self and still manage to color inside the lines.
But whenever you want to remember that you're not a robot, it's fun to take the mask off and look at all the expressive mayhem you caused. It's usually better with the mask off.