绠短汲深

My ability is unequal to the given task,for you cannot use a short rope to draw water from a deep weel

拴捅的绳子很短,却要打深井里的水,比喻能力薄弱,难以胜任艰巨的任务;也比喻学识浅薄,不足以领悟深刻的道理。也作“短绠汲深”