To avoid the social consequences amongst your peers? Perhaps that's not an issue in Norway, but it's an issue in the US.
I don't want my coworkers to know how much I make because if I'm making substantially more or less than them, it will affect how they perceive and interact with me.
I don't want my coworkers to know how much I make because if I'm making substantially more or less than them, it will affect how they perceive and interact with me.