When I wrote my first book, I didn't know that writing and publishing involved so many undertakings, other than writing. Marketing is a full time job and demands a lot of skills I don't possess. Yes, you can engage professional people to do it for you but that costs a lot of money. If you're a self-publisher you might need editing assistance, proof reading, help with cover picture and design. Luckily, I'm a former photographer and commercial artist, thus don't feel the need of the latter kind of assistance.