It’s possible to fix a broken voice. It’s possible to fix one that is pretty skewed. It’s possible to fix one that’s just a little bit off base.
It’s possible to wreck a perfectly fine voice. It’s possible to take one that is slightly skewed and skew it more. It’s possible to take a voice that is slightly off and make it slightly off but in a completely different way.
It is possible to take someone who can sing very well, almost leave them alone, give them absolutely minimal instruction, and see continuous improvement, not based upon the teaching but on the ability of the singer.
It is possible to take someone who can barely sing and, through the skill, care, patience, determination, kindness and persistence of the teacher, help that person learn to sing decently and be very happily satisfied.
It is possible to take someone who can sing decently and help that person become a very excellent singer with a wide range of control and skill, through a combination of determination on the part of the singer, on the part of the teacher and of natural ability of both.
It is possible to take someone who sings really well naturally, and through terrible teaching, demoralization and negative evaluation, take away all of their natural ability and kill the joy of singing such that they never ever sing again, let alone study.
It is possible to take someone who can barely sing and kill any chance the person might have of learning to sing by simply saying to the person, “You have no talent, you will never sing, so don’t even bother to try”.
It is possible to mistake a vocal health problem for a technical problem, thereby compounding things on both sides.
It is possible to mistake a technical problem for a health problem by simply not knowing when to refer a student to a qualified otolaryngologist.
It is possible to assign problems with singing to a technical issue when it is something being aggravated by speech and the speech issues are ignored or, worse, not noticed as issues at all by the singing teacher.
It is possible to sing effectively and have a good career with no training in singing of any kind, but only if you do not sing classical repertoire.
It is possible to sing effectively and have a good career with a flawed voice, as long as the type of music you perform doesn’t require you to expose the flaws.
It is possible to have a very beautiful voice and be absolutely unable to express any kind of genuine emotion in it while singing, which will make you boring and unlikely to have a career.
It is possible to have a very unattractive voice and be so emotionally powerful when you use it that no one really cares how you sound (unless you are a classical singer, in which case, you have to at least stay in that ballpark).
It is possible to sing in a way that shouldn’t be possible because there is so much wrong with how it happens and what it sounds like, but somehow or other it works anyway.
As you can see, the possibilities are endless.