Derek Sivers makes a great point, illustrated by an engaging story:
There's a big difference between being self-employed and being a business owner.
Being self-employed feels like freedom until you realize that if you take time off, your business crumbles.
To be a true business owner, make sure you could leave for a year, and when you came back, your business would be doing better than when you left.
This is absolutely correct, and, as Derek mentions is straight out of Michael Gerber's E-myth book. Gerber makes a number of other points. I strongly recommend reading the book.