In my book, Seven Steps to Inner Power:
“Mistakes are not harmful in and of themselves. What is harmful is our attitude towards mistakes. But, if you are willing to make mistakes, look at them, regard them as feedback, and keep right on making them until you achieve your goal, then you have the right attitude. You don’t purposely make mistakes, of course. But because you are challenging yourself, be aware that mistakes are a natural part of the process.”
