Whenthegoinggetstough，thetoughgetgoing.为什么一个用gets

When the going get tough,the tough get going.
艰难之路,唯勇者行。
the going,并不是指的一类人,而是情况,所以谓语动词用单数。
the+形容词表示一类人,动词以复数形式出现；the tough指勇者，所以谓语动词用复数。

The phrase is a play on words involving idiomatic (Proverb) and distinct meanings of "go" and "tough." In context, "the going" means "the situation," "gets tough" means "becomes difficult," "the tough" means "people who are strong or enduring," and "get going" means "become fully engaged." Taken together, the meaning of the phrase is "When the situation becomes difficult, the strong will become engaged."
The phrase is an example of antimetabole.
Another interpretation could mean, "Those who act tough and proud will vacate a situation when it becomes difficult lest they be proven not as tough as they appear to be."