Has giv'n a man two Bags to bear;
That which his own default contains
Behind his back unseen remains;
But that which others' vice attests
Swags full in view before our breasts.
Hence we're inevitably blind,
Relating to the Bag behind;
But when our neighbours misdemean,
Our censures are exceeding keen.
Source: Smart: Fables of Phaedrus 4.10.