One common trap for sound designers is trying to fit in sounds for everything that makes noise in a scene. This is usually an attempt to make it all sound realistic. This can be a trap and may not even be the most realistic way to handle your mix.
Recently, my mom decided it was time to get hearing aids. Because I was the biggest supporter of the idea, I went to the appointment with her.
At the appointment, they told her that she had to wear them all day, not just when she had company over or when she was watching TV. She needed to wear them for quiet activities too. This was to help her get used to world noises so her brain would learn to ignore them. If she only wore them occasionally, her brain would be overwhelmed by too many new sounds at once, and she could miss something important.
Well, they were right.
The first weekend after she got her hearing aids, I went to visit her. She started telling me about everything she was able to hear. She could hear the refrigerator in the kitchen. She could hear her fingernails on the fabric of the couch. She could hear her pants as she walked.
My mom started just running her fingernails on everything around her to show me all the sounds she was hearing. They were all novel again. Her brain was learning to tune them out.
When I hear sound designers talk about how many sounds they are able to play at the same time, it makes me think of that first week with my mom. They are trying to figure out how to get the sounds of footsteps and clothing in with the dialog and guns and explosions.
Now, it makes sense to hear footsteps and clothing sounds when you are in a quiet room. But the brain learns to ignore those, especially when there is something more important to hear (like an explosion).
You are responsible for what the character should be hearing, as well as what they should not be hearing.
So, the next time you are mixing a battle, and you have over 50 simultaneous sound already playing, take the less important sound out so your player can focus on what you really want them to hear.