The psychology behind this is that we tend to hide within us things that we find unacceptable for a number of reasons. We carefully conceal it under covers of denial and justification lest we feel convicted by our own sense of self-esteem. These are generally movements that attract us but they seem to contradict our sense of right and wrong. We simply put them out of sight by shoving them below the carpet. But then they show up through the back door like the stink from the waste we dump into the backyard which we think is coming from the house next door.
This happens because we are well aware of the movement and the attitude behind it and hence are quick to detect it in others. It is equally true of good qualities. We recognise the good in others that we carry in ourselves. To give an example a miser recognises miserliness in others. A calculating person believes that everyone is calculating and that there can be no uncalculating giving. He cannot recognise what he has not experienced. So too a fraudulent person doubts even a genuine intention and a arrogant person looking through his lens finds in others arrogance much more often.
To give an even more concrete example, men who cast lustful looks on women and try to conceal it under specious names often keep their wife and girls covered completely because they believe everybody will look upon them lustfully. Violent people often feel that they are victims of other’s aggression and hence justify their own. The sadhu who is busy counting the sins of others under the cloak of righteousness see quickly in others what they are holding back in themselves.
Affectionately,
Alok Da