Running a business isn’t necessarily exclusive to entrepreneurs. People in a relationship, with (or without) their own family, are also at the head of their enterprise. There are specific rules, expectations, and tasks to complete. Even without receiving a paycheck at the end of the month for successfully running your family incorporated, there is still an incentive to manage it as well as you can.
Entrepreneurs with another business, next to the business mentioned above, have to manage both simultaneously. Potentially extremely difficult.
If both companies go well, super smooth sailing. If one out of two is experiencing distress, the temporarily suffering business might drag the other down. If both are doing bad, brace yourself.