system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we feel so much better when we hit the "perfect" temperature in a shower even though it is such a small change in temperature?
gpt
Some points about showering and temperature: 

Water is quite conductive of heat. It will absorb heat from you quickly if it's cold, and warm you up quickly if it's warm. 

Water in the shower is moving which makes it even better at changing your body temperature. When you are swimming and not moving around much, for instance, there will be a layer of warmer water near your skin which means heat is getting pulled out of you slower than it might otherwise. In the shower, that layer is constantly getting washed away, so you are in constant contact with the water close to the temperature that's coming out of the shower head.

Water has a huge heat capacity compared to anything else with very few exceptions. 

Add this all together, and you have a very good way of changing your body temperature in a hurry. I'll make no comment on why it feels so much better, but these are some of the reasons why a small change in water temperature makes it feel like a large change.