Why is it called Knight and Day?

Knight and Someday

... would have been a nice title

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There is a sense in the fact that every message has its own reply link!

So long story short:

His real ID is Knight.

They needed a pun.

Hence Knight and Day.

Of course the imagery of night and day suggests the two worlds the two lovers live in, his shadowy world (but he is the chivalrous knight), and hers the world we take for granted and don't feel we need to hide from anyone in.

The movie is romantic pap (I love it), so the Knight motif is ever present, and entirely appropriate in the title.

Ultimately, who gives a @$##$.

Roy's mom introduces herself to June as Molly Knight when June brings the pistons and gets wet. So I suppose his real last name is Knight.

Tom Cruise's birth name in the movie was Michael Knight

Knight Rider did the puns better.

Extremely valid question