The fear of failure is the greatest challenge anyone faces. Not just in learning how to draw, but rather in every facet of our lives. Many people are accustomed to feeling that failure is something terrible, to be abhorred and reviled. That's simply not true.
Failure is an inevitable, natural and necessary part of learning a skill. It shows us where our weaknesses and where we can improve. Without it, we become stuck.
To fail is to be alive - so if you're not failing, you're probably doing something wrong.