Mercedes has been my "difficult" child during our homeschooling. A classic Taurus, she thinks that everything she does needs to be done perfectly. So she puts a lot of pressure on herself to do her schoolwork perfectly the first time.
I kept trying to explain to her that I didn't mind her making mistakes - everyone makes them - I just wanted her to learn from them. She wouldn't write because she's a "creative" speller - ie, she spells like my dad. I wanted her to get her thoughts on paper, and then we would correct spelling later.
Finally, today, she brought me her narration on Heidi that she wrote. I corrected her spelling and asked her to re-write it with the correct spelling, grammar and punctuation - and praised her to the skies for just doing it. Same thing with her math. I explained what she did right (she set up the problems correctly) and what she did wrong (forgot to borrow/carry). She left to do her work beaming.
I reminded her of one of my favorite lines from my favorite movie, Meet the Robinsons - "From failure, you learn. From success, not so much."
Don't be afraid to make mistakes. The only time mistakes = failure is when you fail to learn from them.