Trivia: When Sargent Todd's combat and military record appears on screen, just before the title "between wars" is shown, you can see his different decorations. They refer to Kurt Russell's acting roles: "Plissken patch" (from "Escape from New York/LA"), "McReady" ("The Thing"), "Cash Medal of Bravery" from "Tango and Cash", and "O'Neil Ring Award" from "Stargate" where he played Jack O'Neil.
Trivia: Kurt Russell only has 104 words of dialogue in the entire film.
Trivia: When the veterans are shown leaving the ship to go and set up an outpost on Arcadia, in the foreground you can see a nameplate on some debris. It says "Lewis", from the Lewis and Clark ship in Event Horizon, another Paul WS Anderson movie.
Answer: Emotions aren't just learned. Some are inborn and can't be fully suppressed.
Greg Dwyer