Imagine you are at a cocktail party. The room is crowded, people are coming and going, and you can barely hear your friend as they tell you some juicy gossip about the date they went on last week.
The fact you can still follow what they’re saying is down to your brain performing some very complex operations amid all that noise. Out of all the sound waves reaching your ears, it is successfully isolating the one of interest while filtering out the rest.
