Lies.

 Firstly, AWESOME PIC

And now for the serious stuff..
One of House's key recurring motifs is that "Everybody lies".
This isn't cynical, it's true.

The only thing that is constant in humanity, (note the "in"), is the extent to which we can deceive ourselves. We can rationalize anything, anywhere, anytime. We can convince ourselves that it is good to murder Jews, Palestinians or Tutsi. Indeed, given enough of a nudge in the right direction, based on half-truths and myth, we can convince ourselves that WAR, is good. (e.g. War on Terror).

Coming back to House, it seems that nearly every show has a disillusioned husband, wife, mother, son, father, niece, or close friend. I began to think, that really, they shouldn't be shocked. Everyone has secrets, everyone lies. Everyone hides. and Everyone dies.. (hey that rhymes)..

The lies go two ways, We convince ourselves that we know the other person well enough that they would trust us with their secrets too. We lie to ourselves in the face of all logic. One lie could not succeed without the help of an another.

For example, If Wife & Kids think husband can't have AIDS, it's because that not knowing their father/husband would mean some implicit de-efficiency in ourselves. It would mean we do not know them as we'd like to think. So we deny that they could have AIDS. Because we, ultimately, do not want to feel bad about ourselves, when logically, it's not even our fault.

Why ?

Hell, I don't know. No one does. Cue "It's the human condition" explanation.