It has happened a few times in my life where I install a new shower curtain and hooks, and then constantly struggle trying to pull it open, because the metal hooks get kind of stuck on the metal bar.
When I moved into my new place, it occurred to me that metal on metal usually needs to be lubricated in some way. So I sprayed a paper towel with some WD-40 and wiped it along the top of the shower bar.
My shower curtain now zips along the bar like the Eurostar!
I rocketh.