Don't cry over spilt milk. - Aesop

Every man carries Two Bags about with him, one in front and one behind, and both are packed full of faults. The Bag in front contains his neighbours’ faults, the one behind his own. Hence it is that men do not see their own faults, but never fail to see those of others.

An Eagle swooped down upon a Serpent and seized it in his talons with the intention of carrying it off and devouring it. But the Serpent was too quick for him and had its coils round him in a moment; and then there ensued a life-and-death struggle between the two. A countryman, who was a witness of the encounter, came to the assistance of the Eagle, and succeeded in freeing him from the Serpent and enabling him to escape. In revenge the Serpent spat some of his poison into the man’s drinking horn. Heated with his exertions, the man was about to slake his thirst with a draught from the horn, when the Eagle knocked it out of his hand, and spilled its contents upon the ground. One good turn deserves another.

The most dangerous enemy is the one within.