Because you can always come back stronger and become successful next time. Because your number of tries will never ran out and you can always reclaim what you think is rightfully yours.
People are not afraid of losing itself, they are afraid of the emotions that losing can give to them. They are afraid of pain. Losing is literally just an emotion, it can't kill you nor hurt you physically so why be afraid of it?
Losing can make you learn, the more you lose.. the more knowledge you acquire. You will know your weakness, you can become smarter next time and that is if you take it positively and accept it without being bitter about it. You can dwell with it for hours but not for days.
Losing will make you stronger, you will not be afraid of it anymore especially if you lost a lot. It will not be a big deal and you don't feel anything about it anymore.
If you are afraid to lose then don't even try because for sure you will not love the outcome of your performance. You have to face it and you need to experience a lot of it to become a better person than yesterday. If you are afraid of losing then you will never be able to show your strengths because you are holding back so much, you are stopping yourself from winning.
The next thing about losing is winning, just endure it for a while and you will taste the victory in some other time, maybe tomorrow, next week or next month or even next day. So be happy about losing for the meantime because winning is the next in line.
Never count the time you lost because just like I said it is nothing and it will not make you a bad person if you lost several times. You will only lose your confidence if you count your lost, just keep trying, pounding and growing.