I may also add it is the excuse no art instructor worth his or her salt would ever accept either.
When I use to hear the rationale ‘but I worked really hard on it’ I would always have to throw some water on the fire with this: ‘Your work being good is not a function of it being hard to do, it is a function of it being a good idea well executed, whether it took a year, or a minute.’
People don’t like to hear that. It is natural to want some credit for doing something difficult. And you should get credit, but it is direct credit. If you do something difficult the reward is ‘I am proud of you, you did something difficult’. The reward isn’t indirect. It doesn’t guarantee that what you created with difficulty is good.
It is especially hard to have this attitude with your kids, and it is heartbreaking to see your child do something with hard work and lots of sweat, only to find they got a C or a no comment, or even a harsh critique. But if you are helping them in the best way possible you will praise their hard work, reassure them of the good that is actually in the work and start to teach them the lesson that hard work doesn’t guarantee success, but it does guarantee progress and insight.
If you do that, then their self-esteem will not be attached only to their successes but to their failures and setbacks as well. And THAT is when their self-esteem will stay with them forever.