I read an intersting article about how many SMEs are started as home businesses while they still have jobs.
These people then practice until they are confident and then leave their jobs and launch the business formally. I have seen this a lot in South Africa, but not in the complete form. Rather they stay and have 2 incomes. If the husband and wife are both doing this, and I have seen that quite often, they now have 4 income streams.
There is an obvious ethical problem with those who stay in their jobs, but I suppose it is a reality that is hard to overcome.
Personally, I believe that these type of people could be highly successful if they applied themselves full time to the running of their own businesses, and that they are wasting their talent in this way.