There are Mysterious Victories. And There are No Mysterious Losses
This is one of the kendo sayings I love. This basically is trying to tell us not to become arrogant or no to think that we are better than others because we beat others or did better than others.
It is so true that there are many victorious moments and defeating moments both in kendo and in life.
Even when we win a match, pass an exam or win an important business deal, we should always try to keep us humble because becoming arrogant and showing off our victories won't improve us at all.
Training hard is a part of elements to win. But everyone (hopefully) trains hard. So after all we do not really know why we can win.
However, we always know why we lost. We can go back and think why we lost. I am sure most of the time we can find the reasons why we lost. I always do.
So losses are very important because they tell us things that we can improve. The most important thing is that we learn from them and improve. Don't just ignore. Learn from it!
Hope this helps.