Why do people always forget things?

I would say one of the main reasons people forget things is because they're in a hurry when they're doing something. This makes it easy to forget things, especially important things. Another reason could be bad habits that contribute to forgetting things.

Interesting question, actually. I would say the reason for individuals forgetting their things is maybe being in a hurry, which results in forgetting things, especially important ones. Not thinking about everything you need before going out to a place and not checking that you have everything in your pockets could be the reason for that.