More importantly, existentialism doesn't say that this isn't real. To the contrary, it says that this is the only thing that is real. This world, right here, right now. There is no god or afterlife or set meaning to our lives. We can either see the meaninglessness of the world and crumble under it or we can create our own meaning. Its coming to the realization that we are completely free and completely in charge of our lives that is terrifying. We choose how we live, and have to deal with the consequences, there will be no God or third party to protect you or guarantee your salvation.