This was said to me by my undergrad voice teacher in a moment of frustration. The technique of singing is something one spends a lifetime perfecting but it is easy compared to getting out of your own way. There is a difference between knowing what to do and knowing how to do it and there's an even bigger difference between knowing how to do it and being able to do it. In singing you need to be aware of your mind's patterns so that you can change them. You need to be able to practice concentration and detachment and you have to be able to let go enough to allow singing to happen. So, if you are stuck, if there is something about the technique of singing or auditioning or performing that you can't quite get - stop, breathe. It probably goes deeper than you think but the solution will probably be easier than you think once you stop banging your head against the brick wall.