I was going to separate this into two posts (mostly so that I didn’t have to strain on more ideas), but they are related. Both are about what people believe. Even if you aren’t making up a whole new world, you may well wish to develop mythology and/or religions for your characters.
Perhaps, like me, you are hesitant about making up religions for your characters. Nothing wrong with that, but it is a good way to make your character a separate person, rather than an extension of yourself. That’s always something to be wished.
So, what’s the difference between religion and mythology? Well, people believe religions, but know myths are false. Or do they? I’m sure everyone’s heard of urban legends, also sometimes known as urban myths. While some are obviously false, I’m pretty sure everyone has fallen for at least one at some point or other. Besides, the myths we read today, Greek, Norse, Egyptian, all come from their religions at the time. Maybe they knew some of them were stories, but they worshiped those deities. Okay, myths are stories to explain things, like creation stories. Except that there are many educated religious people who believe in one of those ‘creation myths’. I know I don’t like hearing stories I believe being referred to as myths, and I doubt you do either. It appears to me that the difference between myth and religion is where you stand. My belief is the truth, yours is religious, and his is myth. Just like, I’m unique, you’re eccentric, he is crazy.
Anyway, I’m not here to get in a huge debate about religion. You have your beliefs, I have mine, and reading mine won’t change yours or vice versa. There are four basic divisions in religious belief. Polytheism is the belief in many gods. Henotheism is the belief of one main god over many little, less powerful gods. Monotheism is the belief in one God (almost always capitalized). And Atheism is the belief that there is no god, yes, that is religious because it’s something that must be taken by faith. Anthropologists who have studied this much more than I have; claim that early civilizations almost always start out with Polytheism, with Henotheism or Monotheism coming later. They won’t always change, there are civilizations and religions today that are still Polytheistic. But it means if you are writing a sword and sorcery fantasy, or some kind of primitive society, you may wish to go with the belief of many gods.
This can add many layers to your story, even if you don’t go too in-depth. For one, your characters may be concerned with appeasing or angering one or more deity. You need your character to do X when Y seems more logical? Maybe Y is against that characters religion, or they have taken a vow to the gods to do X. Religious misunderstandings and conflicts are problems in real life, why shouldn’t they be an issue in your story? There are layers of language, both to bless or curse.
Now, the pitfalls. If you are making up a religion or a mythology, you likely don’t believe exactly what your character believes. Okay fine, but are you making your character seem like an idiot for believing this? Your readers will know you made up the belief system, unless you are using a real world religion or mythology as a close basis (not recommended in most cases), so we know you aren’t trying to get us to believe this, but you can, and probably should treat it respectfully. Unless part of the point is your character is an idiot, supposed to change beliefs, or this is a satire of a known belief system, why not treat this as if it is a reasonable belief for the people of that time and place?
Secondly, research is very much your friend. Research as many different cultures myths and religions as possible. If you only know one, than that one is going to affect what you create. If you only know the Greek myths, you’ll likely create something similar, or try doing the opposite to be ‘different’. Why? Because it’s hard to think in other directions. Your head deity will probably be a male sky god, unless you try subverting one or each attribute, like making it a female earth deity. If you’ve read several, then your mind think on different tangents.
Geography plays a role in beliefs. Every religion and mythology (minus atheism) has a story of creation, of how people came about, and what the afterlife is like. I exclude atheism, because they believe death is the end. There is usually a belief that there is one after life destination for those who were good in life, and a different one for those who were bad or evil. Cultures in the tropics believe that the afterlife for the evil is burning hot, while cultures in colder areas usually believe that the afterlife for the evil is freezing cold. Missionaries to the Norse learned quickly to describe Hell as a very cold place. In fact, the name ‘Hell’ comes from the Norse goddess of the Underworld, Hel, who reigned over a frozen realm. (There’s your trivia fact of the day.) People groups that are near each other will have some similarities in belief. The Spartans had the same deities as the Athenians but they were slightly different. Even the goddess of beauty, Aphrodite, had a warlike aspect. Ares was considered of only medium importance and respectability by the Athenians, but the Spartans valued him enough to perform human sacrifices to him. No, I didn’t know that either. If your people group live next to the ocean, then whatever deity controls the seas will be a dominant part of their life. If they live in the mountains, they’ll probably more more interested in the forest or mountain deities.
Another thing to consider is, in your world, are the gods you made up real and how active are they in the lives of mortals? Are they interested in striking down those who insult them? Do they answer prayers? Do they care at all? Do they watch mortals like some people watch reality TV? Yes, you don’t want to have the gods intervene and save the day when you’ve entangled the character beyond their ability to fix things. That’s called a deus ex machina. Literally, god out of a machine. Also known as really bad storytelling and ways to anger all your readers. But if your character prays for something and gets it, is it the gods, or a coincidence. Or perhaps you don’t want to make that clear. That’s fine too. Or maybe the gods are willing to grant your characters request, in exchange for… Or maybe one god does grant the request, which causes problems with another deity. Those are questions only you can answer. It may not even be something the reader knows. But you should.
This is getting long, so I’ll cut it off here. Maybe at some point I can talk more about this.