Philosophical realism is the idea that there is an objective reality that exists independently of our beliefs. I think philosophical realism is obviously true, and it always surprises me to find out there are people who don't (which includes nearly 20% of professional philosophers).
However, there is a sense in which non-realism actually makes sense.
For example, money. There is almost nothing useful you can do with a dollar bill. What few things you can do with it (like burning it for heat) can be better achieved with other, more readily available materials (like wood). The only reason money is valuable, is because people believe it's valuable. We're willing to trade useful items for money, because we know everyone else is also willing to trade useful items for money, not because the money itself is useful.
Many things in society are like that. The leader of a organization is the person whose orders are followed, and people follow the orders of the person they believe is the leader of the organization. Laws are what police and judges enforce, and police and judges enforce what they believe the laws are. Art is whatever people believe art is.
I'd go so far as to say that most people's experiences are shaped more by these socially subjective facts, than by physically objective facts. Maybe that has something to do with some people's rejection of even physical realism.