It’s unlikely you’ll lose it all, but suppose you write a clever app — maybe a cvs editor.

Suppose you find out your cvs editor infringes on a patent and you’re liable. Suppose some business suffers data loss and sues. These things do happen in Europe too.

Also, it’s just a matter of professionalism. A sole proprietor isn’t very professional and many medium-size businesses won’t do business with sole proprietorships.