Pain is weakness leaving the body

[Jessica]

Pain is weakness leaving the body
The above is a piece of propaganda used by the US Marine Recruiting office to get more people to join the marines. Its also figuratively true, and very effective in their commercials.

[PussyCat]

A saying of the US [Marines]
The more pain a Marine endures, the stronger he becomes.
If a Marine feels pain after working out, it means he had a good workout and physical weakness is leaving his body.