Failure and success remind me of the Chinese
yin yang concept. The concept of yin yang is used to explain the interdependence and complementarity of opposing forces in nature and the universe, and to illustrate the importance of balance and harmony in achieving overall well-being. In trading like the op said it helps to create harmony of our emotions and to have a clear head when trading.
Nothing can go as smoothly as expected, that means that each of us must experience ups and downs. Even a businessman will not be as successful as he seems without ever failing or at least losing money financially, that also applies to traders and investors because they both involve money. The successful are those who keep trying after failing, those who get up after falling until they finally find balance.