On the one hand, the earphone ears are related to the balance between the left and right brains, on the other hand, it is the problem of the earphone itself. A complete piece of music contains human voice and equipment sound, so you need two earplugs to reflect it separately. You can try. If you only wear one earphone, you can't hear some music, so you need two earplugs.
Summary: A single earplug will not damage your ears and hearing, and a pair of earplugs will make the sound you hear more perfect, but don't wear headphones for too long and pay attention to protecting your hearing.