ㄊㄡˊㄅㄧˇㄘㄨㄥˊㄖㄨㄥˊtóubǐ‑cóngróng

投笔从戎
  1. 後漢書列傳記載官府為生因為不甘庸碌一生長嘆大丈夫應當效法介子邊疆建功立業怎麼生命長久虛耗?」文人從軍投筆從戎」。 青年紛紛投筆從戎國難」。

to lay down the pen and take up the sword (idiom)​, to join the military (esp. of educated person)​
Ban Chao