An error was originally a journey, not a judgment. Latin errare meant 'to wander' or 'to lose one's way,' and error described the act of straying from the path. A traveller who took the wrong road committed an error in the most physical sense. The metaphorical leap to mental mistakes was natural: to err in thinking was to wander from the truth, just as one might wander from the road. English inherited the word through Old French in the 13th century, by which point the mental sense already dominated. But traces of the older wandering meaning survive in English. An errant knight was a roaming knight, not an incompetent one. Erratic behaviour is literally 'wandering' behaviour. And aberration — from Latin ab- ('away') and errare — describes a deviation from the normal course. The entire err- family maps a single idea: departure from where you should be, whether on a road or in a line of reasoning.