I'm not sure why "you just need to be able to sell" was down-voted. At this time, his comment was the only one mentioning the obviously most important part of "freelancing."

Yes, all those other things mentioned here are important as well but I don't think anything is more important than being able to sell.

You need to be able to find clients and sell to them, but that's not all there is to selling. Selling is also important in being able to set good rates or project fees.