Over the Counter Zinc Additive

Until all of this Zinc hoopla started, i had no clue just how a flat tappet cam Really work. And realize just how few do or did.
I stopped at one of my buddy house, where he was replacing the cam on his dad truck for the second time(breaking in cam failure)
I proceeded to educate him on the importance of ZDDP. He proceeded to tell me that the same cam lobe had failed on the original as well as the replacement. Going on how brand X was a pos and he went to xyz for this cam. he proceed to tell me how bad the lifter was and how difficult it was to remove.
I ask him if it turn smooth in the bore, look at me puzzled and said a.......yah it goes up and down after i clean up the scratched.
I explained about how the lifters, are Not actually flat, that the cam was ground on a slight slop, to cause the lifter to spin in the bore, and that if the lifter STOPPED!,...... the cam would fail instantly.
I Reached down and twist the lifter in the bore and it turned but it felt like it was turning in sand paper.
I help him clean the bore up and reassembled it.
That was too year ago and and its still running today.
The lobe doesn't just slide across the lifter, it way more complicated than that.
But, before, the failure started happening, the simple statement was all we need to understand, about a flat tappet cam to install and make it live.