"Tread lightly" is an admonition you can run into here and there. Weighty things can change the shape of the universe. To use the image in "Herkimer Inquiries" (a great story; thanks for the rec, sovay ), they're like bowling balls on a mattress.

I sometimes think about that in the context of interactions with people. How weighty people leave impressions on others. Which is also reminding me of the expression in Japanese 影が薄い (kage ga usui), for the opposite phenomenon, literally, to have a pale o...