Can you explain this? I will sit for hours with just a pen and paper and not be able to come up with anything worthwhile ideas or thoughts. What do you do?

I sometimes try using pencil and paper when I'm stuck on a specific problem. For example, if I'm trying to debug an algorithm, I might draw examples of the possible states the data structures could be in to make sure I've figured out all the edge cases.

Also, if I'm working on a project and can't figure out which of a dozen possible things to do next, I write down lists of tasks. These will eventually get transferred to digital form, but I find that circling important things and drawing arrows between them is a lot quicker on paper than messing around with some user interface on a computer, and this lack of friction promotes a state of flow.[1] If I get bogged down with data entry, it's easier to forget an item that came up while writing down another item.

[1] https://en.wikipedia.org/wiki/Flow_%28psychology%29