English Idioms and Phrases: Love is blind
The expression 'love is blind' is used to describe a situation where, as you are in love with someone, you cannot see any of their faults, problems or negative points.
"He is so ugly and very rude, why does Sarah love him? Love is blind!"
In this case the speaker is saying that Sarah is in love with someone and she does not notice that he is rude and ugly.
Another one of Shakespeare's many contributions to the English language, this phrase is first seen in the comedy "The Two Gentlemen of Verona", written around 1590, and was also used in other plays he wrote later.
The quote can be found in Act 2, Scene 1 when Speed says to Valentine:
Because Love is blind. O, that you had mine eyes;
Interestingly, in 2005, a study by leading anthropologist Helen Fisher at Rutgers University studied the brain scans of 17 men and women who were in love and the images showed the same brain activity of a cocaine addict. The brain rewards the body with pleasure enhancing chemicals which in turn reduces critical thinking. Therefore while people could list faults in their partners, the pleasure they received from the experience made these problems seem irrelevant.