There are plenty of good psychological answers here. Here's a philosophical one: According to existential philosopher, José Ortega y Gasset, "true beliefs" are

There are plenty of good psychological answers here. Here's a philosophical one: According to existential philosopher, José Ortega y Gasset, "true beliefs" are very old ideas that we have 'inhabited for centuries' and have come to trust implicitly - without question. What we call "beliefs" are "ideas" (about reality) that function as coping mechanisms. They help us deal with the crisis of 'not knowing'. Both are subject to reinforcement/agreement or challenge from "the world", society or by individuals. We like reinforcement and agreement because it makes us feel safe. When someone challenges our beliefs, it threatens to throw us into crisis. It can make us angry because it goes right to the core of our sense of safety. I think a lot of political i.e. socio-economic, religious and tribal disagreements fall into this category.