Will protein (almost) always stick to the bottom of the pan and then un-stick itself?
Sometimes I cook and the protein (meat/poultry/fish) just slip n slide....
Am I doing something wrong if that happens?
Steel will depend on a couple things. Generally, drier meat exterior, more fat in the pan, and a hotter pan will make the meat less likely to stick to the pan. As the saying goes, "a hot pan is a non-stick pan."
Obviously, Teflon is a slip-and-slide. Well-seasoned cast-iron will act a lot like Teflon.