1) Designing only at full resolution. 2) Too many subjects. 3) Tiny text. 4) Low contrast in dark mode. 5) Title duplicated on the image. 6) Fake emotions. 7) Inconsistent branding. 8) Never retesting catalog. 9) Arguing instead of testing. 10) Ignoring title pairing.
Fix loop
Run every candidate through a free AI thumbnail tester and heatmap, preview at feed size, then A/B survivors. Mistakes become rare when the process is boring and mandatory.