Not thumbnails. Not the app grid on your phone. I’m talking about the workhorses—the toolbar glyphs, the status indicators, the inline action buttons that populate enterprise software, creative suites, and dashboards.
Look at the MacOS toolbar circa 2009 versus today. The old icons were stuffed to the gills with gradients and highlights. The new ones (SF Symbols) are stark. The secret to a legible small icon is . how to make icons smaller
Step back from your monitor three feet. Squint your eyes until the screen blurs. Can you still distinguish the trash can from the settings gear? If yes, you have achieved pure silhouette. If no, the icon is too complex. Not thumbnails
The "small" rendering of a symbol is often a completely different vector path than the "large" rendering. The small version might have thicker stems to survive pixel loss. The large version might have delicate serifs. Look at the MacOS toolbar circa 2009 versus today
This is at work. The human brain is a completion machine. It doesn't need the handle to know it’s a mug. It doesn't need the individual keys to know it’s a keyboard.