Leaving ego aside, there's plenty of societal conditioning that explains this too. The negative feelings you may feel by not knowing something (i.e. in a meeting, or in a class...) can certainly plausibly be connected to being reprimanded for not knowing something. It's definitely the bizarre case that not having an immediate answer for something can result in "losing" an argument. Obviously this isn't the way it should be, but it certainly is the way it is many time, whether that be in low stakes argument about a TV show in a bar or a high stakes discussion about what technology you should use. But it goes back even further than that I think. In many ways, our entire school structure is designed around the idea that your success is tied to your ability to answer questions on the spot. Political debates are the same way, right? The reality is that the answer to every question in a debate should be some version of "well, I'd go and ask my cabinet and consult experts in this area..." So I don't think it should be that surprising that it makes people uncomfortable to not know something.