If after ten tries their son still does not understand "one plus one equals two," they will try 20 times, or 100 times. When one parent gets to the limits of his or her patience, the other takes over.
當一個人已經被兒子磨到了臨界點，趕緊換手，讓另一半繼續下去，免得被激怒，脾氣一發不可收拾。