The latter one helps me to reduce head buzz which is generated by randomly reading HN posts or working on a demanding task.
Reading a book, where I actually need to concentrate on the book, some contents generate occasional mind branches. That means, I continue reading, but I think about something else triggered by what's in the book. Then I switch back to the book realizing "Wait, where was I? I have no idea why I'm reading this, and now I skipped a whole page."
When I make a long trip I also have a lot of time to think. So, my scope of thoughts grows and my mind wanders. Basically that's the mode which potentially might make me very happy or deeply unhappy. Because the scope expands from decisions made in the past to decisions to make in the future. And that's where it hurts most.
Can anyone relate?