Because if you are mistaken, and you're able to see it, you have the opportunity for great progress.
There is no dishonor in being mistaken.Yet there is great folly indeed in being so stubborn that you refuse to admit your own mistakes.
Mistakes can be powerful teachers. By knowing firsthand what does not work you gain much greater understanding about what does work, and why.
If you're not willing to accept the possibility of mistakes, you're not going to make much headway.Though there's no need to purposely make mistakes, there's no reason to live in fear of them either.
Even if you are already effective, there likely are ways to be yet more effective.Even if your mistakes are not disastrous, there is still much that you can learn from them.
Embrace the fact that somehow, concerning something, you're probably mistaken.And in your mistakes, find the wisdom that will take your performance to an even higher level.