Let's say we want to measure an electron. We have a rule: the uncertainty in position (Δx) multiplied by the uncertainty in momentum (Δp) must be at least a tiny constant value (h/4π). If we try to measure the position very accurately, making Δx very small (like 0.0001), then Δp must become very large to keep the equation balanced. Step 1: You focus your microscope to find exactly where the electron is. Step 2: Because you used a strong light to see it, the electron gets 'kicked' by the light energy. Step 3: Now the electron is moving at a different speed than before. Step 4: You now know the position, but your measurement of its speed is now totally wrong. You failed to know both!