Amnesia The Plague
One may think they are a one lifetime entity. One may think they go someplace wonderful when they die. One may think they are a human animal. One may think their religion is right. One may believe in all sorts of odd rituals and deities. Of course, one may be completely brainwashed, actually I prefer Mind-washed, since the brain has little to do with anything.
The culprit behind human and other misery is amnesia. One is immortal, can't be anything but immortal. Over the billions and yes, trillions of years of existence in this universe, Beings have accumulated so many pictures, so many things they wish to remain hidden from view, so many losses and so much aggravation, they began to conveniently forget things. And hoped others would too. Add to this a weapon used in interstellar war one has what exists on Earth and other planets today.
It makes a kind of sense though, one cannot truly die, but one can sure forget. And if real callous, utilize tools and weapons that rape his/her enemies of all identity and memory. What goes around comes around, and in truth, these weapons tipped the scale, they started the plague of amnesia.
There are billions upon billions of Beings sitting around Earth asleep. They are in a kind of apathetic slumber, waiting for a body to become available. Hell, they may sleep for tens of thousands of years, slightly wake, and get "Born". They don't take up any space really and are invisible, so no one really notices them.
As the population of this planet grows, more and more new intellects show up. The day there are no more beings waiting for a body....well the human animal is not much smarter than a cow. The human animal was designed, after all, as Being-ware.
The solution to amnesia, responsibility. One is cause. One did what one did. One receives what one has dished out, no matter what lifetime the dishing occurred. Accept your responsibility for you and your condition. Never assume the viewpoint of being a victim-that's effect and what got you here. Responsibility in combination with admiration will alleviate the mental masses and begin the process of recovering self.
The only reason one "believes in" anything is amnesia. Without that, one either knows or doesn't know.
When your body dies, you'll rise above it and depending on your level of responsibility, will take your desired action such as getting born again with memory intact of the previous lifetime.
As a note, Banks used to have a between lives clause in all accounts. One just had to remember their password to reclaim there funds from their previous lifetime. it was all quite matter of fact.