Rome wasn't built in a day! You don't master a new skill in a day either. if you take a painting class or two or five, you will learn a new technique each time but you aren't going to be a master of the skill.
Don't sit at a class and constantly say things like 'I can't do this". "This isn't right", " I shouldn't have come" etc. All that does is spoil your mood, the mood of those around you and in the end evening the instructor goes home feeling that they have failed in some way.
I go into each class that I deliver with a positive attitude. On my way there I try to think of any areas that will be challenging so that I can have 2-3 ways to tell people to try to complete that particularly challenging part.
Occasionally I am in a room of people who simply get discouraged and then the negative comments start with one person, spread to two and before I know it, there doesnt' seem to be one person saying something positive about their piece. I end up taking the entire drive home trying to figure out where I went wrong.
My advice to students:
Go to a class knowing that you might not have a masterpiece worthy of display in a gallery. However, you will learn at least one new technique and go home with your masterpiece worthy to display in your home whith pride that you did it yourselft!