Turning a blind eye is an idiom describing the ignoring of undesirable information.
The phrase to turn a blind eye is attributed to an incident in the life of Admiral Horatio Nelson.
Nelson was blinded in one eye early in his Royal Navy career. In 1801, during the Battle of Copenhagen cautious Admiral Sir Hyde Parker, in overall command of the British forces, sent a signal to Nelson’s forces giving him discretion to withdraw. Naval orders were transmitted via a system of signal flags at that time. When this order was given to the more aggressive Nelson’s attention, he lifted his telescope up to his blind eye, said “I really do not see the signal”, and his forces continued to press home the attack.
Despite the popular belief that he was disobeying orders, the signal gave Nelson permission to withdraw at his discretion.