Power
You have the power to make or break your business. After all, you're the artist; these are your babies you're putting out there to sell. You have power over the quantity, the quality, the prices, how efficient and polite you are when you respond to your customers and ship your items, and whether or not you decide to hire someone to help you.
What you don't have power over is whether or not people like your stuff enough to buy it. Sorry, Shmoopers. You know what they say: You can lead a horse to water, but you can't make it want a hand-knit ski mask, no matter how cool it is.