Błędnie: Allowing him to leave with the children was nothing but shear stupidity. Poprawnie: Allowing him to leave with the children was nothing but sheer stupidity.
"Shear" to 'strzyc', 'przystrzygać', 'nożyce'. "Sheer" to 'zupełny, całkowity, kompletny', a także 'stromy', prawie pionowy'.