Because of what we now call the "fog of war" (and Sun Tzu called the "muddiness of war"), both sides in any contest tend to see reality as they choose, through the filter of their own theories. Where is there hard fact? Which theories are really workable? Sun Tzu teaches that the truth is found in the "trifling details," that is, the smallest, most detailed solid evidence. These details may seem so small that they seem unimportant, but Sun Tzu teaches us that we must change our theories when the smallest solid fact that doesn't fit our existing theory.