Why do you assume most people think the way you do?

Whatever you believe, your gut quietly adds: "and most people agree with me."

The false consensus effect is the habit of overestimating how many people share your opinions, tastes, and choices. Your own view is the easiest example your mind can reach, and the friends, family, and feeds around you mostly resemble you, so you treat that small slice as the whole population. The more a belief matters to you, the more common you tend to assume it is - and the more you suspect anyone who disagrees of being odd, biased, or just wrong.

You hate pineapple on pizza and feel sure "almost everyone" agrees - but half your office orders it without a second thought.

Your sense of what "most people" think is really just what the people near you think - a sample, not a survey.

Before saying "obviously everyone agrees," check whether you've actually asked anyone outside your bubble - it keeps you from misreading a room, a market, or a vote.

False consensus = you mistake your circle for the whole crowd.

Learn the idea and practice English at the same time.