What does 망양보뢰 (亡羊補牢) literally mean?

 ANSWER: Fix the [sheep] pen after losing the sheep.

The Korean expression 망양보뢰 (亡羊補牢) literally means "lose (亡) the sheep (羊) [and then] fix (補) [the sheep] pen (牢)." It is similar to the English expression "close the barn door after the cow has gotten out," but while the English expression suggests that it is too late to fix the problem, the Korean expression seems to suggest that fixing the problem after the damage is done will at least stop it from happening again. In other words, the Korean expression seems to suggest that it is never too late to fix a problem, at least according to the Korean video below.

From Dong-A's Prime Korean-English Dictionary