ANYONE WITH A passing familiarity with American daytime television knows “The Newlywed Game,” where fresh-faced young husbands and wives flub basic personal questions about their spouses, revealing an often comical ignorance about each other’s habits, beliefs, and sexual quirks. In many cases, the newlyweds seem to grow visibly apart on-air, and after the laughs die down it’s hard not to be struck by this cluelessness about a person that someone has pledged their life to.Would most of us do any better? What if we played the same game with our longtime friends? If researchers who study relationships are to be believed, the surprising answer is no.A growing body of experimental evidence suggests that, on the whole, we know significantly less about our friends, colleagues, and even spouses than we think we do. This lack of knowledge extends far beyond embarrassing game-show fodder - we’re often completely wrong about their likes and dislikes, their political beliefs, their tastes, their cherished values. We lowball the ethics of our co-workers; we overestimate how happy our husbands or wives are.