system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does a computer gradually start to slow down and stall after a 2 or 3 years use?

Yes macs are included in this. That's the reason I'm asking this question. My mac is definitely noticeably slower than when I bought it in October 2008. It just stalls loads. Can anyone explain this?
gpt
Imagine you have a sweet **Legacy of the Wizard** thermos.

You use it everyday for school and it's your favorite container.  One day, you put Cherry EXPLOSION Koolaid in it, drink it up and have red teeth all day long!

The next day, you put in Dr. Pepper.  You don't like Dr. Pepper as much as daddy does (at least, he *calls* it Dr. Pepper), but it's one of your favorites, huh?  What's cool is that the little bits of Cherry that were still in there made it taste like CHERRY EXPLOSION DR. PEPPER.  WOW!

Each day, you try a different drink (or even the same ones from time to time).  After a while, what happens to your thermos?

It gets all gross and gooey, huh?  All slimy and smelly.  Even though it smells kind of sweet, it all still is just too covered in gunk to be usable.

So, what do you do?  You wash it, of course!  After you get your mom to put it through the dishwasher, it's fresh and ready for you to use again... as long as you keep it clean, slugger.

* thermos = computer
* fluids = programs / various other data
* dishwasher = formatting, defragging, scandisk
* your mom = HOT

*edit*: Fixed bulleted item list.