mó​chuān​tiě​yàn

persevere

磨穿铁砚 (磨穿鐵硯) mó​chuān​tiě​yàn
persevere
to persist in a difficult or long-term task with unyielding determination
study diligently
to study with great persistence for many years, literally wearing down an inkstone through constant practice

Frequency

Written text
0.002 per million

Sources

Definitions
CC-CEDICT
Frequency data
BCC Corpus (BLCU)