Actually, we human beings do that quite a bit. That's because there's a different between proximal and distant "goods."
Let us take an example.
I know that lying to my wife is bad -- it will harm our relationship, make me a bad person, and put us both into a mode of discourse in which we are deprived of access to reality relative to each other. Bad, bad, bad.
But my wife asks me, "Do you like this new dress."
No, I don't. It looks like an explosion in a toilet paper factory, and is an entirely unflattering garment in every possible way. And if I can see that, so will others. But her eyes are shining, and she seems thrilled with her purchase, and anything I say about the dress will all too easily transfer into a criticism of her person or her taste...the easiest way out consists in me lying to her, or at least evading the truth cleverly.
So what do I do? I do want a good and honest relationship with my wife. I know that lying will damage that, and is not the route to get me there. But I also want not to create a conflict, or to seem mean, or to spoil her moment of happiness with her new purchase...
So for many people, the answer would have to be, "Lie now, and feign ignorance later." You won't damage your relationship with your wife (too much), and you'll avoid an uncomfortable situation now.
But what happened to my commitment to realism, and to truth?