At first loud sounds can sound very loud, but after a while they might not sound so loud anymore. Using an electrical drill for the first time without hearing protection sounds really loud, but after a while the sound is more bearable. Playing the drums for the first time sounds awfully loud, but after playing for a while, the loudness isn’t as bothering.
There are multiple things that happen. First is a temporary threshold hearing shift that happens when ears are exposed to loud noises, after a while the ears lose some of their sensitivity to sounds and things don’t sound as loud anymore, this is temporary and after some time without noise, it goes away. Second is perhaps a subjective shift of loudness perception. Third is hearing damage that appears after loud noises, often from repeated exposure.
This can create a dangerous circle. Someone starts listening to music and sets the volume to high, after a while of listening a temporary threshold shift occurs and the music doesn’t sound as loud anymore, because they want it to sound loud again, they increase the volume even more, another perception shift happens, volume gets increased again. If this goes on for longer, eventually hearing damage from noise happens. It is very important to try protect your hearing anytime you’re exposed to loud sounds.