Suppose it's just you. You are the only one to work on the basement. Maybe, like me, you're wife is pregnant or just had a baby. Or maybe your husband is overseas. Or maybe your partner, friend, cousin, neighbor just plain isn't interested in this type of project. This is not a big deal.
I would say that you can do 90% of the work completely on your own. Using the tips below, I think the drywall stage is the only spot where you must have more than one person. You will get a work-out though. That's one of the benefits of finishing your basement on your own - free weight loss and muscle building.