There are some practical subjects that you can only learn them with a teacher or an instructor. For example, if you want to learn driving a car or some jobs like medicine and engineering and some sports like skiing and swimming, you’ll have to find a teacher. It’s almost impossible and inefficient to learn those things on your own. By the way, if you are going to learn some things by yourself, you may learn and understand them incorrectly! For example, from my own experiences, after I had started learning playing the guitar without a teacher, I got used to wrong habits regarding strumming and tempo, but after finding and learning with a tutor and identifying and eliminating those incorrect habits, I was able to play properly.