Possible interpretation: When a situation is difficult or dangerous, strong people work harder to resolve the problem. This saying relies on a difficult play on words; it could be rephrased word-for-word as: "When the situation becomes hard, strong people start working."
Note: the going (noun): the situation; the ground; the environment | tough (adj.): difficult, hard | the tough (noun): tough people; hard, strong people | to get going (verb): start; go Origin: This saying is attributed both to Joseph P. Kennedy (1888-1969), father of the USA President John F. Kennedy, and to Norwegian-born American football player and coach Knute Rockne (1888-1931). Variety: This is typically used in American English but may be used in other varieties of English too.