Imagine you are in the boxing ring. Across from you is your opponent. You're both sizing each other up knowing that when the bell sounds you'll be toe to toe throwing punches.
The bells sounds and you move forward. Suddenly, just as you are ready to attack, twenty of his friends climb into the ring to offer their assistance. You have no where to go. You have to fight.
Such an experience would be devastating to anyone's confidence in their ability to fight and win. Being outnumbered in this way is enough to crush anyone to the point of potentially laying down right there to just take the beating.
Now imagine that after those twenty opponents showed up, one of your own friends showed up, or perhaps two, three, or enough to match them one for one. Your friends would suddenly level the playing field and reduce the fight back to just you and your opponent.
In life, you are going to find that you will add opponents to your fights by allowing doubts to enter your mind. Every doubt you have questioning whether you can win is another fighter standing across from you that you have to go through to get to your real opponent.
Everyone gets doubts from time to time - you are no different. What can set you apart is what you do with it.
When a doubt arises in your mind - use it to make adjustments to your game. Quickly analyze the doubt and see if there is any justification for having it.
Don't ignore it. Leave it alone and it will fester and grow into more doubts. Soon you will have twenty new opponents to fight before you even get to the real threat in the other corner.
When you start to doubt yourself and your abilities, look at it objectively. Often just by questioning why it is there is enough to make you realize it has no basis in reality and it will disappear.
Of course that only works if there is no real basis for your doubt to be there. If you didn't train as hard as you should have or aren't in fighting shape or have an injury that didn't heal and you're fighting anyways, then come to terms with what is about to happen. You may win, but you're going to fight every one of those nagging doubts and your opponent.
Systematically defeat every doubt that enters your mind when you climb into the ring. Do that and you make it that much easier to win.
Suddenly, it will be you and twenty friends vs your opponent and not the other way around.