What does "it's not rocket science" mean — and why is it funny?

informal

Meaning

A way of saying that something is not difficult and should be easy to understand.

Where it comes from

A modern phrase. Rocket science stands in as the popular shorthand for the hardest, most baffling kind of work imaginable.

Why it is funny

The humor is the gap it draws. Whatever simple task is at hand — stacking a dishwasher, say — gets measured against launching spacecraft, which makes the comparison both reassuring and a little mocking.

Used in a sentence

"Just follow the recipe — it's not rocket science."