Thomas a Kempis

We must not rely too much upon ourselves, for grace and understanding are often lacking in us. We have but little inborn light, and this we quickly lose through negligence. Often we are not aware that we are so blind in heart. Meanwhile we do wrong, and then do worse in excusing it. We take others to task for small mistakes, and overlook greater ones in ourselves. We are quick enough to feel and brood over the things we suffer from others, but we think nothing of how much others suffer from us. If a man would weigh his own deeds fully and rightly, he would find little cause to pass severe judgment on others.

You will never be devout of heart unless you are thus silent about the affairs of others and pay particular attention to yourself. If you attend wholly to God and yourself, you will be little disturbed by what you see about you.