Vocals are by far the most difficult instrument to master because we all speak the language and understand the voice. The bar is way higher for a vocalist than a drummer or a guitar player etc. There are many pitfalls to singing because we all learn to speak the language first. Unfortunately, you can not sing the same way you speak, though most people try. Learning to sing Is like learning to cook in a dark kitchen. You must learn how to find where all the ingredients are before you can even start cooking. Then you have to learn how to mix those ingredients together and prepare something people actually want to "eat". Every teacher should have no shortage of metaphors and similes. This has never been more important than with a vocal instructor. Unlike teaching an instrument like a guitar you can't just point with your finger to the problem. As a vocal teacher, you have to get inside someone's head and expand their thought process.