There will always be the rare person who learned on their own,but dont try it! For every one who did it ,a thousand smashed up the plane.
A good instructor will also wean you from the common bad habits new fliers will tend to adopt,and instruct you in the safety aspects and etiquette of flying with others.As a club prez and instructor myself I will go to all lengths needed to help a begginer,but I have short patience with the new person who insists they are qualified having learned themselves or with a simulator and dont see why they have to take our wings program test.(safe takeoff and landing,approaches,1 loop,1 roll.horizontal 8,R&L procedure turns)