Let's see if we can keep this simple and practical. Here's the list of why most of us can't sing as well as we hope.
1 - We are trying to use our favorite singer as a reference - doing this inextricably leads to trying too hard and becoming easily frustrated. Just like you can't look exactly like someone else (even if you wear make up, do your hair and have surgery done) you can't sing exactly like someone else (even if you stylize your voice, use tension and change your vocal approach). The solution is to understand that you are a unique individual who has a unique voice. You can't sound like your favorite singer just like your favorite singer can't sound like you! Be fair! (This is usually an extremely difficult pattern to break)
2 - We are not released enough - the most common reason for not developing our true potential as singers is because we are too tense. The big muscles (arms, shoulders, chest, stomach, back, legs) are usually tense... these are somewhat easier to release through stretching and movement. These big tensions usually lead to forcing the voice, something that doesn't go well with the tiny, tiny vocal cords. They just don't work well when forced. Even harder to release, and more subtle are the tensions in the neck, tongue, jaw, mouth, lips, face and throat. If these muscles aren't release there will be great difficulty for the vocal cord to operate well with the air. These are extremely hard to detect and subtle tensions when one isn't being guided by an excellent teacher. The solution is to release the body, neck, jaw, tongue and throat -- this can be hard to do because it will inevitably expose all our vocal inabilities. A teacher can be of immense help in the area.
3 - We are not developed enough (our vocal cords are not flexible enough, strong enough and coordinated enough) - if your vocal cords aren't developed enough, with a good balance of the high and low registers, the is no way you will be a great singer. There is no way to develop the tiny muscles within the larynx if you are not released enough. If you haven't released enough to insure that the vocal folds are getting all the attention and development you will never develop the voice. You have got to overcome all unnecessary tightness in order to really start developing. There is no two ways about it. We may not be happy with how we sound when we have released it all, we might crack, sound weak, thin, whimpy, shaky, uncoordinated and very crappy. This is when the TRUTH of the matter gets exposed. Most of us are way too afraid to allow this radical exposure to happen -- this is why most of us never learn to really sing well. We are just too reluctant to hearing the truth of our released voices. The solution is to RELEASE and allow the muscles within the larynx to work independently and develop. If we never allow this, we never really grow. It's that simple.
Okay, that's about it. Another point that's critical to mention is that the role of the analytical, rational mind in this is simply to remain quiet and do nothing. Ideally, this is an entirely experiential process, it's got to do more with sensation and it is a very objective and natural process. Our analytical minds just tend to jump in and judge, condemn and distract us. It takes a highly objective and mature person to be able to bypass the ultimately useless comments of the mind and stay focused on the HEART of the matter. The most power the analytical mind has is the power to make COMMENTS, which is no power at all. Why? Because the comments have nothing to do with the ACTUAL REALITY. They're just freaking comments!!!
Staying objective and natural is the fastest way to true growth and harmony. If you want to learn how to sing, you have got to shut up and do the work. It's super essential, it will save you years of time and will work like the magic you've always dreamed of. Of course, it will take TIME. Development takes time, no matter what it is we are referring to. How long? Well... the sooner you shut up and do the work, the sooner you'll find out. And when you truly shut up, it won't matter to you!!!