In "In the Midst of Alarms" (1894) by Robert Barr, the author is describing a man who couldn't make a friendly conversation with a girl, although he was usually a good talker:
It flashed across the mind of Yates that this was intended as an intimation that he might see many things outside to interest him. He felt that his visit had not been at all the brilliant success he had anticipated. Of course the quest for bread had been merely an excuse. He had expected to be able to efface the unfavorable impression he knew he had made by his jaunty conversation on the Ridge Road the day before, and he realized that his position was still the same. A good deal of Yates’ success in life came from the fact that he never knew when he was beaten. He did not admit defeat now, but he saw he had, for some reason, not gained any advantage in a preliminary skirmish. He concluded it would be well to retire in good order, and renew the contest at some future time. He was so unused to anything like a rebuff that all his fighting qualities were up in arms, and he resolved to show this unimpressionable girl that he was not a man to be lightly valued.
I can't understand this bolded phrase, or does "know" here mean "admit"?