In our individualistic society, to go "by the book" is often seen as a bad thing. We like to take chances, to color outside the lines, to get out of the box. As such, Life comes with a rather interesting countercultural message: There's a reason we go by the book. There are occasions when we want what's in the box to stay in the box.
About half the terrible things that happen in Life happen because someone literally opened doors that should've stayed tightly shut. Admittedly, keeping those doors shut often doesn't feel like the right thing to do, particularly when an imperiled crewman is on the other side.
But ask folks who save lives for a living, and they'll tell you some pretty sobering truths: You don't dive in to save a wildly thrashing drowning person because they'll likely take you with them. You don't carry someone down from the top of Mount Everest, because if you do, neither of you will make it back. Life adds another example to the list: Best not to mess with super-strong, super-hostile Martian life-forms. We're all about sacrificing ourselves to rescue others … but when we sacrifice ourselves and don't save anyone, well, that's another kettle of crawdads.
Life is a tense, often contrived story—Alien reheated, minus the acid blood. This sci-fi horror story could've easily been a PG-13 thriller without all the blood and harsh profanity, and frankly, it wouldn't have lost a thing. But as it is, Life feels a lot like its Martian star, Calvin: a critter you might not want to let out of the box.