No, you don't need another person to dread up your hair. But it REALLY, REALLY helps. It's very tiring to try and reach around to the back of your head for long periods of time, you know? Your locks will also probably end up looking a lot nicer if you have someone help you out because they can see where the next one should be, how big they should be to fit your head properly etc. Try and get someone to help if possible, you'll be glad you did.