书到用时方恨少shū dào yòng shí fāng hèn shǎo

指书平时就要多读，免得用时才感到读得太少。
【例】人说“书到用时方恨少”，我后悔转业当时没有上大学。要是上几年就不会像现在这样。(冯国仁《草原有座小屋》)

书到用时方恨少

平时不多读书，等到实际应用的时候，才感到知识和学问不够用。

书到用时方恨少shu dao yong shi fang hen shao

it is when you are using what you have learned from books that you wish you had read more books than you have

书到用时方恨少

it is when you are applying what you have learned from books that you wish you had read more;you regret your deficiency in learning only when it comes to applying what you have learned