At its core the Real Estate sale itself is no harder than the sale of a car or the sale of groceries.

They give you the money, you hand over the receipt or title and the goods and they walk away with it and you walk away with their money.
 
You really could just meet with a buyer accept their money sign the deed and walk away.

          That leaves out how you find your buyer.
               That leaves out how they get you the money.
          That leaves out the inspections and certifications they will ask for.
               That leaves out the sales contract.
          That leaves out the negotiations.
               That leaves out the marketing, 
                    the advertising,
                    the showing, 
                    the house preparation, 
                    the market analysis
                    the title company, 
                    the title insurance, 
                    the house insurance
          and a myriad of other details and things that can go right or wrong with the sale.

Real Estate companies, brokers, and agents exist because with the most expensive sale on the most important property in ones life, it helps to have a professional involved.

In a sellers market some sellers find that they can sell their house themselves and save time money and hassles. But even then most of the time, the buyer has a professional working with them. Even then though frequently the single professional is doing what two professionals would take care of.

In a normal market, or a buyers market, buyers find that they have numerous choices of homes and a real estate agent allows them to see more than they would see otherwise. As sellers find that time of a typical sale and the cost incurred rise, there are fewer and fewer buyers without agents, and they use a professional as well.