I don't, of course! All I know is that I looked at what was for sale, and I evaluated the situation in my own mind, without considering what other bidders might be thinking; I hid my thinking from them. Had I placed a public bid, I would have made my thinking public, and I would have allowed his thinking to color mine. There's a lot to be said for that, and it might have been much to the sellers advantage, but I did not see the upside for me. By cutting off any unintentional communications with other bidders, I was able to stick to my initial assessment of the auction.
This is not the ideal situation for everyone, but there are times when it is to the buyer's advantage. And I'm okay with that.