Hi Anibal!
The exception to this that you didn't mention is that self-employed people can actually make money while they are not trading their time for income. This includes residual and passive income, as well as royalties. These kinds of incomes are more common for those who are self employed, but not exclusively. But, yes, for the most part, self employed individuals do need to be "on the clock" to earn an income.
BTW-I just followed you. (My first follow). : )