Not everybody has been given the gift of a golden voice as well as not everybody has the skills to do so. While it is true that many can sing according to what their definition of singing is, not all have the capability to endure singing exercises.
Personally, I have been to many singing exercises and sessions. I don't have such a great voice to start with but I stick to the workshop from beginning until the end. I have been to neck level pool of water at 4AM in the morning just to practice a piece while I am shivering in the cold. I have been singing while my legs are up in the air. And most of all I have been to the strictest of all strict professors. While you may think that it is too much, I would disagree and say it was never enough.
It really matters for singing neophytes to build all the confidence they can muster and learn how not to limit themselves only to the songs they think they are good at singing. It is surely the quickest way to bore the audience to death. Because of this, flexibility comes second in the priority. Singing is like a constant challenge to your pride and confidence. It shakes your firm stand. It makes some tough people quit. Believe me; I have seen so many walk out of the door in anger and frustration because they cannot do one piece of song correctly no matter how much they try.
You need to hear what you sing to be able to tell where your mistakes are and go on improving them from there. During the first few hours or perhaps days of the workshop, I already can pinpoint where I actually stand or what mistakes I have already committed just by listening to my own voice. Many people will really think that listening to their own voice is embarrassing but to tell you the truth, those who listen to their own voice will actually find many things they can improve on. Certainly, it takes time to get the hang of it and be familiar with the techniques. You can never find anyone who perfects one piece of song with only minimal practice and vocalization. Even the music geniuses perhaps have to do one piece over and over again to be able to obtain that perfect harmony.
Just like in any other aspect of life, you will find it hard to please everyone. Same is true with music. Some other people will like what they will hear from you while some others will not and maybe even despise what they can hear. But don't get discouraged if you hear people say you are otherwise because you have to remember every musician, singer or composer has their own way of expressing their music and it is up to you if you let minor criticisms go into your head. Unless you don't want your music career to become a success, don't listen to what other people will say. Just do your own thing.