Keith Johnstone in Impro for Storytellers (Chapter 4, "Spontaneity") observes:

... I might tell them about Kimon Nicolaides, who taught life-drawing, and who said that 'The sooner you make your first five thousand mistakes the sooner you will be able to correct them.' Then I might add, 'Learn to ride a bike on grass so you don't lose any skin, and stand facing a bed when you learn to juggle so that you don't have to keep chasing the balls, and always try to improvise with people who understand that it's okay to screw-up. And remember that if you succeed brilliantly, you'll depress the rest of us, and then we'll never get any volunteers.'

_{(cf. Make Mistakes, ...) - ^z - 2013-04-18}