How did John Thornton feel about the bet BEFORE Buck pulled the sled?

From the text:

He did not know whether Buck could start a thousand pounds. Half a ton! The enormousness of it appalled him. He had great faith in Buck’s strength and had often thought him capable of starting such a load; but never, as now, had he faced the possibility of it, the eyes of a dozen men fixed upon him, silent and waiting. Further, he had no thousand dollars; nor had Hans or Pete.