Not having a strong understanding of the market from the get-go and not having an employee to run the business after 6 years is correlated in the following sense:

Founders have a large amount of surface area to cover (office, accounting, insurance, payroll, legal, taxes, hiring, management, etc). If you are in a market that doesn't allow you to grow quickly enough to hire in a large enough team to cover these functions (plus the meat and potatoes of the actual product and customer requirements), you can be left stretched extremely thin. If founders are covering 15 different company functions, it hard to find someone who can handily take over.