One of the best accidental discoveries I've made is the book Beautiful Oops! by Barney Saltzberg. I've used it this year as an ice breaker activity for all of my classes, and the kids LOVE IT as much as I do!
Beautiful Oops! shows students that, not only are "mistakes" okay, they can become beautiful works of art! Older students especially (2nd grade and up) are so hard on themselves, and this wonderful gem, accompanied by my constant nagging that a "perfect" work of art is as mythical as a unicorn, helps them loosen up and be much more flexible and patient with themselves when some element of their artwork simply refuses to stay the course.
Class use: I read the book with students on the first day of our class, letting them explore the pictures and discover for themselves what can be found in the "oops" on each page, and then students create a "beautiful oops" of their own! (We use 18"x24" manila drawing paper, crayons, and markers.) I also put the book in my "Inspiration Station" center, and when students finish their work early they can peruse the book on their own.
I can't stress enough how wonderful this book and the personal "beautiful oops" experience are for helping students loosen up and not worry so much about "mistakes." The part I love most is witnessing a student get upset about a tear, a "wrong" color, or any number of problems that can arise and hearing another student jump right in and say, "Don't worry! It's just a beautiful oops!" It really is a beautiful thing!
If you'd like to explore more of his work, here's Barney's website.
There's even a musical video preview of the book! :)