"Do not judge, or you too will be judged. For in the same way you judge others, you will be judged, and with the measure you use, it will be measured to you. "Why do you look at the speck of sawdust in your brother's eye and pay no attention to the plank in your own eye? How can you say to your brother, 'Let me take the speck out of your eye,' when all the time there is a plank in your own eye? You hypocrite, first take the plank out of your own eye, and then you will see clearly to remove the speck from your brother's eye. -Jesus

It's human nature to have difficulty seeing your own weaknesses. In fencing we have a saying, "A good fencer knows his strong points and how to use them, a great fencer knows his weaknesses and how to use them." It is difficult to be objective about your own work as you always put a bit of yourself in it and it becomes personal.