Humor gráfico: Think!

(El alumno) - No sé como resolver esto. 
(El profesor) - Bueno, piensa. 
(El alumno) - ¡Oh Dios, qué idea! ¿Por qué no se me habrá ocurrido antes?

(The student) - I don't know how to solve this.
(The teacher) - Well, think.
(The student) - Oh God, what an idea! Why wouldn't it have occurred to me sooner?