system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do ballpoint pens sometimes stop working at a specific spot on paper?

I often find a ballpoint pen will stop writing but be able to write just fine on a different spot of the paper. Even if I keep switching back and forth to two different areas, sometimes I can never get the pen to work in a spot.
gpt
Ballpoint pens needs friction to cause the ball to roll and deposit ink. If a part of the paper has been smoothed down (for example by unsuccessfully using the pen, or by some glue) then it won’t roll and there won’t be any ink laid down. Because it’s dependant on the surface of the paper it will consistently happen at the same spot.