Explain How Noise-Cancelling Headphones Actually Work

You wear them daily and have never actually known how they work beyond 'noise goes away'. This explains what the headphones are doing to the sound waves, how they detect the noise around you, and why cancelling is different from just blocking, using one everyday comparison so it actually sticks.

Explain how noise-cancelling headphones work to someone with no background in physics or audio engineering. Cover what sound waves are doing, how the headphones detect outside noise, and how they cancel it out rather than just blocking it. Use one everyday comparison to make the cancellation mechanism click. Keep the whole explanation under 200 words and avoid technical jargon unless you immediately explain it.