What is common knowledge in your field but shocks outsiders?

More than half the CO₂ emissions of the industrial age have been dumped into the atmosphere since 1990.

@davidho That the results of your spin were decided before you even pushed the button or pulled the handle on that one-armed-bandit. When I tell people the math and reality behind slots they are actually offended that I'd question their ability to "win at the slots". I don't work in that particular domain anymore, but it's still pretty funny to see the superstitious struggle with the facts of math and blatant emotional manipulation.