Theory and War’s Friction

In reading Rick Atkinson’s The Day of Battle, I came across a passage from the official British military history of the allied operation at Salerno, Italy, in 1943 [emphasis mine]:

In the land of theory…there is none of war’s friction. The troops are, as in fact they were not, perfect Tactical Men, uncannily skillful, impervious to fear, bewilderment, boredom, hunger, thirst, or tiredness. Commanders know what in fact they did not know…Lorries never collide, there is always a by-pass at the mined road-block, and the bridges are always wider than the flood. Shells fall always where they should fall.

It seems to me, when analyzing a commander’s performance, or divining his intent based on subsequent events, too many American Civil War writers live too much in the land of theory.