Kotowaza of the day: But can you walk the walk?

Japanese:

畳の上の水練

Romanized:

Tatami-no ue-no suiren

Meaning of Japanese:

Swimming practice on the tatami mat

English equivalent:

Knowledge without practice makes but half an artist
A mere scholar, a mere ass

Related:

(verb) much, or just read about it?
Armchair quarterback, etc.