a barber learns to shave by shaving fools

US /ə ˈbɑːr.bər lɜ:rnz tə ˌʃeɪv baɪ ˈʃeɪv.ɪŋ ˌfulz/
"a barber learns to shave by shaving fools" picture
1.

理发师通过给傻瓜剃头来学习剃头