When you were a child your parents took you to the beach and collected a little jar of sand for you. They put it on your nightstand so every morning you would see it and remember your trips to the beach. It was a very special jar of sand.
But every night while you slept, the Sandman came and stole a grain of your precious sand. You didn't notice at first. Who could notice one grain of missing sand? But the weeks and years went by, and one morning you woke up and noticed there was sand missing from your jar!
What happened? How did it disappear?
Your hearing is like that jar of sand. And every crash cymbal hit, every hammer strike, every engine rev, all the loud noises that damage your hearing are like the sandman coming every night to steal your sand. One morning you might wake up and notice some hearing is missing!