Thomas R. answered 09/25/19
Over 25 years of experience and a sense of humor about math
Yeah, this is one of his more subtle ones, isn't it? Most of his advice makes excellent sense, even if it sometimes needs explaining first. What he meant this time was that an enemy crossing a river might be trying to draw you close so a hidden force that crossed earlier -- say, in the night -- could ambush you while the larger force closes in from the river.