For example, I waste at least 2 hours a day on the weekend on HN. I learn a little bit, but not as much as if I had been actively trying to learn a new technology or topic. Also on HN, I get frustrated with others' responses, so it affects me mentally as well. If anything is engineered to be addictive for those in tech, it's HN.
Also, news. I can read news sites for hours. Constantly going back to the same headlines, waiting for something new.
And games. I have a handful of games I'll waste time on.
And deal websites. I want to save money.
The only way to stop all of it? Stop using my phone and computer.