I've never fully understood. While the full context makes it clear that it's a bit of an evasive Humprey Appleby non-answer to the question, I doubt many people

I've never fully understood. While the full context makes it clear that it's a bit of an evasive Humprey Appleby non-answer to the question, I doubt many people have ever heard the full context, and in any case evading questions asked by journalists is more or less a universal trait among politicians and political appointees. The best explanation I can come up with was that at that particular point in history there was a large ready-made audience who wanted something to make fun of Donald Rumsfeld about, and when that unusual quote came along they started repeating it among themselves until they managed to convince themselves that it was hilarious and that it totally confirmed all the bad things they already believed about Rumsfeld. Like a cat with a caption or a Russian guy singing "trololololo", it's not especially funny on its own, but if everybody around you thinks it's hilarious you can pretty much convince yourself of its value. A more contemporary example would be Sarah Palin's (entirely true, and somewhat relevant to the question being asked) claim that you can see Russia from Alaska. Many people seem to think this is hilarious and proof that Sarah Palin is an idiot, without really knowing why. (Don't get me started on the large number of people who apparently think she claimed to be able to see Russia from her house...) edit: In the interests of balance, I'll also mention that Al Gore's supposed claim to have "invented" the internet makes more sense in context, and even Bill Clinton's musings on the meaning of the word "is" is (or rather was) a perfectly reasonable attempt to split a semantic hair.