Stress
When you've got orders for two hundred hand-knit ferret cardigans but only have three of them in stock because you really thought the kitty earmuffs were going to be a bigger hit, you'll know what stress is.
When you've put hours and hours into your hand-carved picture frames and nobody is even visiting your shop, you'll know what stress is.
When your wheel-thrown vases were doing great, but suddenly aren't selling at all because that snotty new seller, MyVasesAreBetterThanYours7760, is undercutting the competition with inferior products that have totally uneven glazing, you'll know what stress is.
Being self-employed is extremely stressful. Long hours spent working all by yourself are lonely. Only having one set of hands makes it super-hard to get big orders done on time. You have no control over whether or not people buy your products. And unlike a nine-to-five job, you don't have a guaranteed paycheck or benefits.
It can take years to turn a significant profit. Years. During that period, you'll still need to pay for things like food and rent.
Better set an extra plate out at dinner, because stress is going to become your constant companion.