Could God be
a figment of our imagination?
How do I know that I haven't invented God based on my own desire for him to be true? It's been said that God created man in his own image, but maybe we have created God in our image since it makes us feel better psychologically. Believing God to be true allows us to escape the desperation of the idea that "life stinks and then we die."
Wishing for something to be true or getting psychological benefit from a belief doesn't make it true.