The army tries to instill will power in its new recruits. When privates get tired and want to quit running, they are encouraged to think "mind over ....." and keep going, which they often can.

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The army tries to instill will power in its new recruits. When privates get tired and want to quit running, they are encouraged to think "mind over ....." and keep going, which they often can. (*) mass (*) nature (*) aches (*) matter

This is a companion discussion topic for the original entry at https://english.best/questions/12761,the-army-tries-to-instill-will-power-in-its-new-recruits-when-privates-get-tired-and-want-to-quit-running-they-are-encouraged-to-think-mind-over-___-and-keep-going-which-they-often-can/