If you're thinking about learning to play guitar or bass by watching video lessons on YouTube or someplace similar, or if that's in fact what you are already doing, you should know that you're only getting a fraction of what you could be getting with live one-on-one lessons. While the quality of information you can get from a live teacher is likely to be far better than anything you can get in a video, most of the difference lies in the 'coaching' you should get from a teacher (sadly, not all 'teachers' do an adequate job in this area). There are four broad categories for which a teacher is responsible:
Undoubtedly the most obvious reason you might look for a teacher, 'information' involves the passing along of knowledge and the performance/offering of demonstrations. For example, being told about key signatures, and being shown chords and scales. For the most part, this is what you can get from any book or video. The problem with these mediums is the necessarily rigid method of communication. A live teacher, on the other hand, can answer your questions and provide alternate ways of explaining something, and thus make it easier to learn. This dynamic way of learning is reason enough to get a teacher instead of relying on videos, tabs, and illustrations; but there's so much more you can get from a good teacher that you'll never get from a book or video.
You've watched a video or read a chapter, but how well did you learn the lesson? Did you misunderstand something, or even forget to do it? How well are you executing what you have learned? Videos and books can never help you answer these questions. All you can do is repeat the lessons over and over again, hoping to catch something you missed or are doing wrong. A good teacher will watch you attempt what they have taught you and point out where you've gone wrong. Passing along information and providing demonstrations is one thing; seeing how well you received that information or learned from those demonstrations is another matter.
You're never as bad as you think you are (and very likely, never as good as you think you are). Almost every book, video or service is marketed to make it seem like you can easily play the instrument if you just follow the 'simple' steps outlined in their lesson or program. Unfortunately, these sales pitches leave the average novice wondering what's wrong with themselves for not being able to do what is presented as so simple. The result being discouragement, and ultimately, quitting the instrument. A good teacher, on the other hand, can tell you if you're on the right track and encourage you to continue, or as the case might be, that you could be doing better and prod you forward.
Surfing around someplace like YouTube offers no guidance or order to your learning whatsoever. As the saying goes, 'you first must learn to crawl before you can walk'. Obvious as this is in everyday life, many beginners are fighting this basic premise when teaching themselves with videos. And while books and programs offer direction, they lock you into a path of learning that might not be the best for you (or good for anyone, as is too often the case). Many different factors determine how lessons should unfold. What are your interests? Do you have any prior experience? Have you had an injury to your hand(s)? The possibilities are many. Books, videos, and programs are one-size-fits-all. Live lessons, though they share many common topics, are tailored to suit your abilities and desires.
Live lessons are not a necessity. There's a lot of stuff out for free that can help you. But if you really want the best you can get, a personal teacher is the way to go. Give it a try so you can appreciate the difference.
Visit vmsmusiclessons.com for information on in-home lessons (available for those who live in Suffolk county New York) and live online lessons via Skype.