Certain metals like stainless steel, aluminum, and titanium will rapidly form a thin hard oxide layer on their surface. It is this layer that prevents further corrosion. If these oxide layers abrade off by friction, the "bare" metal surfaces can adhere and pull metal from the surface. Also, if a new oxide layer then forms while the bare metal is in contact, it can become seized.
I believe it was S&W that solved the problem of galling in the machining of stainless.