刀不磨要生锈，人不学要落后
dāo​bù​mó​yào​shēng​xiù, rén​bù​xué​yào​luò​hòu

continuous learning

刀不磨要生锈，人不学要落后 (刀不磨要生鏽，人不學要落後) dāo​bù​mó​yào​shēng​xiù, rén​bù​xué​yào​luò​hòu
continuous learning
a blade will get rusty if it is not sharpened; a man will fall behind if he doesn't study

Sources
Definitions
CC-CEDICT