You use the term ‘Turn a Blind Eye’ to refer to the act of ignoring or failing to
acknowledge something you know to be real.
Example of use: “She knows he’s lying to her, but she’s choosing to turn a blind eye to the situation.”
The origin of the expression ‘turn a blind eye’ can be found in the 1801 naval battle of Copenhagen, when Admiral Horatio Nelson and Admiral Sir Hyde Parker disagreed over tactics. The first recorded use of the phrase as we use it today comes from Martha Wilmot’s 1819-1829 More Letters from Martha Wilmot: Impressions of Vienna: “Turn a blind eye and a deaf ear every now and then, and we get on marvelously well.”