system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some pains "hurt more in the morning" than they do when they occur?
gpt
So these sorts of pains come from an inflammation reaction. 

If you are working out, then small tears occur. These tears do not bother you at the moment because the nerves don't detect them very well and they don't cause anything to drastically change. 

After some time however, the broken cells that are torn leak stuff out that attracts your immune system which normally fights of bacteria and other germs. 

The immune system cleans up the torn tissue and this clean up is what causes the soreness the next day.