false consensus effect

is the tendency to overestimate the extent to which other people share one's opinions, beliefs, preferences, values, and habits.

In psychology, the false-consensus effect or false-consensus bias is an attributional type of cognitive bias whereby people tend to overestimate the extent to which their opinions, beliefs, preferences, values, and habits are normal and typical of those of others (i.e., that others also think the same way that they do). This cognitive bias tends to lead to the perception of a consensus that does not exist, a 'false consensus'. (wikipedia)

false consensus effect, n.All

false consensus effect