What Is the Most Uncomfortable Thing About Backpacks?

https://outdoorsfaqs.com/what-is-the-most-uncomfortable-thing-about-backpacks/
When you go outdoors, you have to carry your stuff in the backpack. If you are forced to do this for hours, no doubt these are the most annoying things that you will notice:
Heavy load.
Sweating.
Load pressure on shoulders and difficult breathing.