Isn't your reality just in your head?
The phrasing of the question makes it "trappy" to answer. Reality consists of what IS even when we aren't paying attention OR agreeing. When we participate in the interpretive function of coloring what IS and reconstruct it into our version--that doesn't change THE reality--it changes our feelings and actions only.
A person confronted with cancer may go into denial of that reality. A misplaced sense of reality may lead them to pursue quack cures instead of mainstream medicine. The fear and desperation (emotions) trump what is practical in that instance.
So, the question of YOUR reality, in the case of the frightened cancer victim, leads to a destructive action/reaction.
If your reality is in your head then your thoughts of God are just as real as anything else maybe more real unless you can be sure you are the creator of your thought process and it wasn't given to you by a higher power. So to believe in God is the start of all reason. No?
No. Examine your premise and how it leads to this conclusion you've stated.
Your statement consists of IF....THEN.
The IF being false leads to a conclusion (..belief in God is the start of all reason.)
Reality is OUTSIDE knocking on our mind. We have to choose to let it come in. If we peek out the window and guess---it is the guess that comes in.
We want a superhero in the sky watching over all things.
Deus ex machina is the plot device that solves all problems---even though it is a flimsy construct.
God use to walk and talk with people, drown them, raise them from the dead and send miraculous signs and wonders---SO THEY SAY.
Since recording devices were invented---isn't it a wonder--nothing more of this sort happens DIRECTLY attributable to proof.
The god myths can't produce in the court an Exhibit A. Even the big gun: THE BIBLE is completely devoid of original documentation.
No--God is more super mystery than super hero.
All this "god" business is the Higher Ignorance at work. It is taking a supposition and inflating it big time into grand FACT.
We cannot know. We can only invent, invent, invent.......and then INSIST, INSIST, INSIST....with a bevy of convenient interpreter's tidying up the confusion (with their hand out and their palms open for loose change.)