I've always enjoyed that the cam surface for that particular push-push mechanism design (click pen) is not that dissimilar from a Leibniz wheel. It's so tempting to add more steps.

https://en.wikipedia.org/wiki/Leibniz_wheel

I can't help myself and have to link some of my favorite youtube channels.

Engineerguy: https://youtube.com/@engineerguyvideo

Chris Staecker: https://youtube.com/@ChrisStaecker