I look at this question in the different light. If we didn't fail (at least a little), we probably didn't expose ourselves to enough risk and fear. If we didn't expose ourselves to enough fear, we chose a safe path. If we chose a safe path, we didn't reach our potential. If we didn't reach our potential, we let ourselves and the people who are counting on us down.
So I say, don't ask whether or not you made a mistake. Instead, ask whether or not you showed up. And showing up is really underrated.
Because if you have the guts to show up again and again no matter how many times you fail, sooner or later you will succeed.
"Your sight-reading course is for me a great pleasure. In the beginning the course took me much more than 15 minutes a day. But now I am exercising the left hand everything is going much easier better and faster. And the same is the case when I repeat the right hand exercises. I feel the sight-reading training will for me be very helpful for my further study." - Willem