Dhammapada verses 33 and 34

33. Just as a fletcher straightens an arrow shaft, even so the discerning man straightens his mind — so fickle and unsteady, so difficult to guard.

34. As a fish when pulled out of water and cast on land throbs and quivers, even so is this mind agitated. Hence should one abandon the realm of Mara.

– Dhammapada III – Cittavagga: The Mind 33 – 34