Develop Your Potential: a good teacher knows when they are working with a student that possesses a great deal of potential. They will work to bring the best out of you, thereby developing strengths in you that you may not have even known you had.
Develop Good Habits: a good teacher is well-acquainted with their instrument. They have become good players in their own right because they have developed good habits around posture, technique and practice. If you practice on your own, you could end up forming bad habits, which you would later have to work to correct.
Learn Faster: though it is certainly possible to learn your favorite instrument on your own, you may discover that working with a teacher helps you to progress faster. It can be challenging to find the right information around any given topic, and your teacher is likely to personal experience in that area that they can relate to you.
Gain An Outside Perspective: when you are practicing on your own, you may feel that you are progressing at the rate you should be. However, your teacher will be able to help you identify problems areas. They are critical enough of their own playing to know when they are making mistakes; therefore, they will be able to tell when you are making mistakes.
Achieve Your Goals: Goals are much easier to achieve when you have someone to keep you accountable. Without a teacher, you may not even set goals. They can help you to determine what is realistic based on your current commitment and skill level.
Access The Right Information: though you can find a great number of lessons related to your instrument on the internet, it can be hard to differentiate the right information from the wrong information. A good teacher should be equipped with the right information to be able to help you.
Remain Accountable: a good teacher will keep you accountable. When you know that you have a weekly lesson to go to at a certain time, you will practice harder to make sure you are prepared for the next lesson. Moreover, a teacher will work to make sure you are doing what you need to do to continue to improve.
Positive Pressure: when you have a weekly lesson to go to, you will have to learn to prioritize and get more done in your practice time. If you like a challenge, this urgency will manifest as positive pressure. A good teacher will have high expectations for you.
Opportunities: your teacher has likely been around the music industry for a while and has probably built up many industry connections. Your teacher may be able to provide you with various opportunities and connect you with people that can help you in your career.
Fast-Track Your Results: because a teacher will keep you accountable, they will also help you to progress at a speed that is right for you. They will help you set goals and achieve them quicker than you could on your own. They will have a good idea as to where to take you next in your development.