Why do people believe "white privilege" is a thing?

@Ladyryan Why do you think that is, Ladyryan?

@NankerPhelge It’s a kind of mindset, white race are more superior than other race, nothing less than that. PTA clubs, work place/job interviews, or at any simple gatherings,

@Ladyryan I've never understood it. I knew when I was in junior school that people are still people regardless of race, so why not treat them equally? I don't get where that mindset comes from.