We soon believe what we want to believe. In World War II we called it ‘wishful thinking’, which is defined in The shorter Oxford English Dictionary as ‘n illusory state of mind towards events which is coloured by one’s wishes concerning the future, especially as to what one hopes will happen.’
The proverb can be traced back to Latin and appears in a slightly different form in Shakespeare’s Henry IV, Part II when Prince Henry says to his dying father: ‘I never thought to hear you speak again.’ To this the King replies:
Thy wish was father, Harry, to that thought:
I stay too long for thee, I weary thee.
Dost thou so hunger for mine empty chair
That thou wilt needs invest thee with my honours
Before thy hour be ripe? O foolish youth!
His Majesty is not so far gone that he cannot deliver forty one lines of rebuke before Prince Hal gets a chance to explain himself.