I hear from many people who tell me that so-and-so never took a guitar lesson, that they taught themselves and they are now an accomplished guitar player. And certainly people like this do exist. But most people who avoid taking guitar lessons with a real-live teacher tend to give up after only a few weeks, or less.
Generally speaking, trying to learn to play a musical instrument on your own will take a lot longer and will likely involve a lot of unnecessary frustration. Here are seven reasons I think you should hire a guitar teacher:
A good teacher will know the best songs and exercises that will help you develop your skills and knowledge as efficiently as possible. He or she can direct you to songs that are appropriate for your skill level -- not too hard so you don't get frustrated, and not too easy so that there's still a challenge and you're learning new things.
A music teacher can (kindly) point out when you're making mistakes. They can also very quickly advise you how to improve your technique within seconds, with just a few words even while your still playing. For example, as a student practices, I can say "third finger" or "remember to shift there" without the student skipping a beat. People who learn on their own often don't know when they're playing a song incorrectly, or when they have bad habits.
Also, people who learn on their own often end up playing songs incorrectly without every realizing it. I've seen countless Youtube "cover song" videos in which people play the wrong chords, or the wrong notes. Without a teacher to point these things out, these people may never know it.
A teacher can show you how to play with proper technique so that playing the guitar becomes easier. Many self-taught musicians spend far too much energy "fighting" with their instruments when they play a song because they did not learn proper technique. They are less likely to ever be able to play as fast, as accurate, and as musical as a person who learned good technique.
An experienced teacher can help you play the more difficult songs because they've been in your shoes before and they've learned numerous tricks that can make a difficult song seem easy. A teacher with over ten years of experience has very likely played all the famous guitar solos from rock history at some point. So they are already familiar with the pitfalls and can guide you through the difficult parts from their own experiences of playing the song.
A guitar teacher is available to you so that you can ask questions. You cannot ask questions of a book, video, or app.
A good music teacher is also your coach -- able to congratulate you when you're doing well and lift your spirits if you're feeling frustrated. Don't underestimate how important this is. In my experience, this is actually one of the most valuable roles of a guitar teacher because students will always have ups and downs. There will be times when the student feels that they are making leaps and bounds in progress, but at other times they can feel discouraged when they take that next step forward and play more challenging music. A good guitar teacher will know when a student needs some coaching through these difficult pieces.
Taking regular weekly lessons tends to provide people with the motivation they need to ultimately succeed and be able to play the songs they want to play with confidence, skill, and musicality. A weekly lesson provides that little bit of pressure that's sometimes needed to keep you practicing.
A teacher can give students specific goals to reach each week -- exercises and songs to practice and learn before the next lesson. Without a regular weekly lesson, it's very hard for most people to stay motivated, continue to practice and learn new songs.