Schoolboy Error: (n.), (der. old English), A mistake, often trivial, clumsy, dimwitted or easily avoided. Generally shameful in hindsight, but without cause for embarassment, owing more to circumstances or instantaneous bad luck, rather than serious incompetence of behalf of the maker. Derived from the "trial and error" psychology present in Victorian-era English public schools.
Upon dropping the soap in the Violent Offenders' Wing of Barwon Prison, Eric cursed his schoolboy error.
Dr. Feynmann lowered his glasses as the fruit of twenty minutes labour yielded an unwanted result: E = mc^2/0. "Well fuck me", he said, turning to the class. "I seem to have made a schoolboy error."