What life hack is so simple yet so effective, you're shocked more people don't know about it?

I have a plastic container where I put all instruction manuals plus hardware that comes with it that I don't need right then. It was very useful when I decided to mount my soundbar a decade after I bought it and knew exactly where the mounting clips and template were. Any time I need to check the manual for specs or something, I just need to look through a pile and will find it.

Agreed. I also paraphrase the instructions in my own words to make them easier to follow later on.