Tā zǒng shuō wǎngzhěbùkějiàn, láizhěyóukězhuī, yúshì chóngxīn kāishǐ xué yī.
He kept saying 'the past can't be revised, the future can still be chased' - and started studying medicine again.
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history
From 《论语·微子》 (Analects, Weizi), sung by 接舆, the madman of Chu, as he passed Confucius: 往者不可谏，来者犹可追 - the past cannot be counselled; the future can still be pursued. 陶渊明 later echoed the pair in 《归去来兮辞》.
usage
谏 is 'to remonstrate / advise against', often used of advising a ruler. Here it is applied figuratively to time: you can't talk the past into changing its mind. Almost always paired with 来者犹可追.
