On the other hand, removing all risks from children’s lives does not leave them feeling safe. Childhood exposure to mild risks fortifies children. Exposure to mild feelings of danger teach children self-confidence. Failure is defragilising. On the other hand, too much security is toxic. It leads to an unconscious expectation that life will always be stable or positive. And it won’t. Toxic Security: Feeling Safe vs Being Safe - Justin Hendriks Psychology

That is, we learn best when we are challenged to grasp something just outside the bounds of our existing knowledge. When a challenge is too simple, we don’t learn anything new; likewise, we don’t enhance our knowledge when a challenge is so difficult that we fail entirely or give up. That is, we learn best when we are challenged to grasp something just outside the bounds of our existing knowledge. When a challenge is too simple, we don’t learn anything new; likewise, we don’t enhance our knowledge when a challenge is so difficult that we fail entirely or give up. So where does the sweet spot lie? According to the new study, to be published in the journal Nature Communications, it’s when failure occurs 15% of the time.

https://www.sciencedaily.com/releases/2019/11/191105113457.htm