Imagine throwing a ball. You'd expect science to be able to work out its exact speed and location at any given moment, right? Well, the theory of quantum mechanics says you can't actually know both with infinite precision at the same time.
It turns out that as you more precisely measure where the ball is, knowing its speed becomes less and less accurate.
This conundrum is commonly referred to as Heisenberg's uncertainty principle, named after the famous physicist Werner Heisenberg who first described it.