The pursuit of perfection is not the same as striving for excellence. If you do not understand the difference, and are becoming a perfectionist in your ballet training, you will jeopardize your progress in different ways. Ballet technique must be excellent. But you need a healthy viewpoint to be consist in your advancement.
Self-criticism is not the same as self-critiquing. A critique is a critical examination of something. But it is more related to a particular definition from the Merriam Webster Dictionary:
"critical may also imply an effort to see a thing clearly and truly in order to judge it fairly"
Self-criticism has a negative slant to it, in common usage anyway. It usually means just plain picking on yourself.
A lot of your ballet technique can actually be perfect. Your posture can be perfect. If it isn't, you can get more flexible, or build strength and make it just right. The challenge in ballet, is retaining the perfect posture when you first learn a harder version of what you are doing.
So, if you are always striving to advance, you are always moving past the point where you feel secure in a movement. That's just the way it works. If you are self-critiquing and not self-criticizing, you'll be happy with this process, or at least accept it.
Perfectionism is a state of true unhappiness. You actually bully yourself. And, if you are learning a physical activity, you bully your body as a result. It is very complex.
There are always bad days and frustrating classes. A healthy viewpoint is one of letting it go and just starting the new day when it comes. You do your best every class, and sometimes your best is a little better than other times.
The healthy pursuit of perfection comes when you know your work and you can do your work, and you are rehearsing with a coach who is going to help you with every minute detail. And that goes way beyond the technical into the dramatic elements, pacing your energy, and the repetition. The repetition that means you can dance beautifully on a bad day too.
Always remember to relax and stretch your muscles, and reflect on the things that are easier for you, that you really enjoy doing in class. It's a given that you will fall asleep thinking about the things that felt not so good. But try to end your thoughts with "but I'm really good at..."
Striving for excellence will not jeopardize your progress. Get the information you need about ballet technique, and you will continue a healthy pursuit of perfection and you WILL get into pointe shoes.