system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:What exactly is going when a ballpoint pen seems unwilling to write in one area of a piece of paper but writes just fine elsewhere?
gpt
You have to get the ball rolling so to speak.


The way ball point pens work is by rolling a ball through ink then onto paper. Pen ink dries when exposed to air, this lets it flow onto the paper then stay there without smudging or making an outright mess, the ball serves not only to transfer the ink in a controlled manner but to seal the unused ink from air. The seal isn't complete though since there needs to be enough space for the ink to get out. When this ink dries it takes a fair bit of friction to break up the dried ink and free the ball to roll and the ink to flow. Even without dried ink there is still a minimum amount of friction that is needed to roll the ball, sometimes there are parts of the paper that are too smooth where as the rest of the paper is fine.