You know you will die. You don't know what happens to you after you die. This presents a problem because the human mind is not comfortable with the unknown, instead preferring to use its creativity to conceive of ideas to cover up the unknown. However, the fear of death does not get covered up by belief, any more than a man falling out of a plane without a parachute can ignore the ground by closing his eyes, and imagining the ground beneath to be made of marshmallows.
So, you psychologically react to the unknown with imagination---this is the fact. The reaction creates a gap which is the space between fact and the pretention of an after-life (or if you pretend as an atheist, the psychological reaction to imagine that there is no life after death creates the pretention). This is sustaining the fear of death because the only way that fear can end is if you do not seek escape from the unknown.
Attempting to solve fear is the perfect way to sustain it. If you are happy to be with the unknowable unknowns without trying to solve them, then you can leave fear alone and live. A tinnitus patient who cannot live with the sound in his ear spends his time seeking treatment and never lives.
You are happy when you get what you want, and to get what you want, you must toil. To be happy often, one must enjoy the toil, because the achievement of wants are seldom, and the toil is often. Therefore, act because of the love of the action, rather than the love of the result. You can love the result, but if the means to achieve the results is something you hate to do, then you will live a masochistic life.
Nobody knows what there is: the extent of the material world, and whether it has always been; or if there is a cause, or if there is a cause of the cause; or if there are an infinite number of causes with no end. Instead of being happy with the unknown, people have imagined Gods, and given those Gods qualities; however, people are not convinced by their own beliefs. Thus, often, in search of more information, they seek other religions, other philosophies, other explanations (in science etc). When a person says God is infinite, he/she admits their own ignorance without realizing it, because the mind cannot know that which has no boundaries (Latin prefix in- (not) + -fini (bounded)).
The brain is a tool for studying the finite and that is the realm of the known.
The men try to control each other by suggesting that the infinite God imposes finite rules upon man, finite rules that benefit themselves. As men invented Gods rules, those rules benefit males. Thus, women are discriminated against in the religious texts. In order to accept those ideas, first you have to read the reasoning as to why women are inferior, meaning that one needs first to be convinced (programmed), as the ideas are not self-evident without reason. Deceivers always utilize reason to bend what is evident into what is contrived, and for that you need books, pulpits etc...
Mankind seeks control via reason, which is the known. As their God is infinite, and they seek to convince you of 'Gods laws' with reason (the known), you can say that mankind has painted over God with his knowledge, in order to suit his own goals.
What there is---if there is anything separate that can be said to be a cause---cannot be known by man (if God is indeed infinite), therefore, it is the desire to escape the unknown which creates the fear. Indeed, the religious teachers implore adherents to fear God (e.g., phrase: "to put the fear of God into him"). Thus religions are not about ending fear, but sustaining it.
It is fear that one is not prepared to give up. As long as you seek to give up fear, so long as you maintain it.