Lets say I decide that – instead of a bonus Feat – humans in my world get Darkvision. I’m planning to run a city-based intrigue campaign with much of the action after dark, and having everyone carrying torches, candles, or lanterns to avoid falling in the gutters doesn’t fit in at all with the mood I have in mind. Just as importantly, Darkvisions limited range means that opponents can easily be out of sight while remaining in earshot, greatly improving my ability to have the characters overhear other groups – or be overheard by them. Specialists may be a little bit rarer – but most specialists are simply expert NPC’s in any case.
And all that’s well and good. Unfortunately, it goes a lot further than that.
When someone asks “What shops are on this street?”, and I casually inform them that there’s “a butcher, a cooper, a wheel-maker, a blacksmith, a candle-maker, and a leatherworker” I’ve got to be prepared for some bright player to abruptly note that candles are rare, special-order, items and that that shop must either be a cover for something or be doing a lot of business with non-humans; otherwise it couldn’t stay in business.
Now, if non-humans are scarce, or the non-human kingdom to the east is hostile, or some such, I may have just sent the entire game off on a random tangent. Worse, if someone spots my efforts to get things back on track, I’ll just feed the notion that “there’s no need to pay attention to the details, the GM will keep us on track anyway”. Say good-bye to investigative scenarios, to trying to deduce what’s going on, and to role-playing. The players will never be able to tell what’s relevant information and what’s just another GM mistake.
There’s nothing wrong with making changes – but you really need to consider their impact on your setting before you implement them or your setting will stop being believable.
The most dramatic example I can think of was from a Champions game: one player literally wanted to try playing God – and the first phrase was “I make ‘c’ (the speed of light) equal to infinity!”. The response was “there is a very bright flash, then everything gets very dark and quiet”, since such a change instantly destroyed the universe in a flash of infinite energy. After a few moments the player announced “I put the universe back!” – to which the response was “there is a very bright flash…”. Announcement number three was “Er… I put the value of ‘c’ back to normal and THEN put the universe back”… After being god for a few minutes – and accidently destroying the universe several more times – the group decided that this was losing its amusement value and went back to the usual game.
What will a few moments of thought tell us about humans having darksight? Well, first, the candle, lantern, and torch-makers will be almost out of business. There won’t be nearly as many accidental fires. Wood will be a bit cheaper, forests a bit less managed, and wildlife likely a bit more plentiful. The population growth rate will be a bit slower and evenings will be more productive. Children will be slightly rarer and more valued. Beekeeping will be less profitable, since there will be less demand for wax, so honey and mead will be more expensive. That might have a secondary impact on crops, but wild bees will probably take up the slack. There will be far fewer mine explosions. Street lights will be non-existent and any torch sconce or lantern-hook is likely to be taken for an obvious secret-door trigger or evidence of a non-human architect. With slower population growth, the Orcs will probably invade the civilized lands more often. Textured tapestries, sculptures, engravings, and reliefs will probably take precedence over paintings and similar works of art which won’t show up well to darkvision. Most sentinels will be able to see perfectly well in the dark – and city guard street patrols will appear abruptly out of the shadows, rather than giving clear warning via their torches. Children won’t be afraid of the dark.
Hm. Even a minute or two really considering this gives me enough material to make this culture subtly distinctive, with a personality all its own. Little details that the players can pick up as they go, and which will serve to give this campaign some consistency and detail – otherwise known as depth. The players will know that mysteries are indeed mysteries, not just errors, and can really feel that their exploring an alien world – not just looking at the backdrop for their next fight scene.
Given a chance, the players will usually help you out. They’ll gladly invent minor details, discuss how things would change, and theorize in front of you. Listen to them, and when one of them comes up with an idea you like, or theorizes about something you’ve forgotten, or spots an inconsistency, steal the idea, let it serve as a reminder, come up with an explanation, or use that inconsistency to lead them to a clue, plot, or mystery that explains it.
You don’t have to go as far as Tolkien and invent distinctive languages for your various races and thousands of years of history for your kingdoms – but wouldn’t you like your world to be as absorbing as his? Consider your ideas for a few minutes, and listen to the players, and they’ll gladly help you make it that way.