One of the most common problems with training the voice has to do with how the singer perceives the training process. Some of us think that we're doing everything wrong and have to start from scratch.
Some of us just let the voice work naturally and try to reinforce strengths and weed out errors that we've built into our singing over the years.
But some of us think that if we're taking singing lessons, then we have to ignore our natural abilities and try to work the voice in a way that's not natural to it. This makes us try to directly control the musculature involved in singing, which should largely controlled by the vowels we use. We search for everything that feels different from what we were already doing before we started lessons.
The result is that progress is slow. Nothing is easy, and there are so many mistakes to correct.