Andres Segovia, one of the finest classical guitarists of all time and a master instructor, once said that "every guitarist is self taught". It would not seem to be in the interest of an instructor to tell people that they are not going to be successful unless they teach themselves, but it's true. To each individual music is a unique universe. Instructors are great for showing the way in a confusing world of methods and techniques by helping to put exercises in the proper order and context, and also matching the right methods with the right person.

The best musicians are the ones that take the information that they gather from instructors, professors, books, the internet, etc and properly apply it in a way that allows them to achieve their personal goals.

So if you're an aspiring musician with a lot of motivation and drive don't be apprehensive about taking some lessons, and if you don't have any motivation or drive don't expect an instructor to provide it for you :)