Also be aware metal sands different to paint and fillers.
Duh
I mean,
Used paper may get your surface rough enough when sanding paint.
But use fresh paper on metal so you get proper surface prep for your primer.
If you have a good magnifying glass you can see the difference in the scratch depths.
It's like traction for tires...lugs or slicks
One you fight to make stick
The other fights to hold on

Give me ambiguity
or give me something else