This rule doesn’t apply to just D&D. This rule applies to all pen and paper, or tabletop, RPGs. I’d go so far as to say it should apply to most things in life but there are times to be serious too.
Let’s not forget these are games. That’s what they are for. Sure they can inform and enlighten but they are primarily to entertain. While the business of games is serious business playing games shouldn’t have to be. So if you are looking to get into Pathfinder, Shadowrun, Tunnels and Trolls, Numenera, Poker, Cricket?, or Dungeons and Dragons always remember the first rule is to have fun.
So why am I telling you this as the DM, or GM if you prefer? If you are running a written adventure in a predefined game system, whether it is from Wizards of the Coast, Paizo, Kobold Press, or any other fantastic third-party publisher keep in mind a lot of systems are merely suggestions. As the rules adjudicator, it is your job to make the final call. Let’s take Tomb of Annihilation for example. The hex crawl can be both the best and worst part of the game. As the DM you can use the random encounter tables to pick what your adventurers face from hex to hex. But you don’t have to. If you want to throw a zombie retching dinosaur at your group go for it. If you sense a pack of undead is going to TPK your party you can tone it down, or you can ramp it up if they are bowling the undead over.
There is also the exhaustion rule to keep in mind. Between the characters mapping out their exploration, worrying about misquotes, water, and exposure to the elements you can start to get bogged down in the minutia of running the game and lose sight of the fact your players are on a grand adventure. Maybe you want to chuck the exhaustion rules because your characters are having a hard enough time keeping up with the guide that is trying to get them lost on their way to Omu and you can sense it’s wearing on them. It’s perfectly fine to do so. The only thing I would caution against is making the encounters too easy on your players. It is possible to go from one extreme to the other. You still want things to be a challenge or you run the risk of losing the groups interest entirely. It’s a balancing act but it’s easier than it sounds. You’ll be able to look around your table and see the looks on your player’s faces and now if you are succeeding.
This can also be applied to other rules as well. If there are a lot of monsters in an encounter it can be cumbersome to roll initiative for all of them. Jeremy Crawford recently on a segment of Sage Advice suggested assigning them all as 10 and let the players roll for their initiative to speed up the process. Don’t be afraid to mess with the system rules. That’s why they are there. Just don’t throw them all out at once.
Short version, if it’s fun keep it. If it’s not fun get rid of it. Don’t be afraid to make adjustments on the fly.
Making changes doesn’t just have to apply to rules as written either. Take a look around your table at the players. I look on Facebook, Twitter, or any other social media platform and I see hundreds of thousands of people having fun. But I also see more than a handful complaining about people who aren’t having fun. It is to the point where I can’t tell if people are just baiting for responses on forum boards or if they genuinely play with a group of people that get their jollies at other’s expense.
If people always cancel, find new people.
If people want to fight and argue about petty issues, find new people.
If people want to pay more attention to their phone or tablet, find new people.
But before you find new people I would suggest that you converse with your fellow players and let them know how you feel and why. Some of them really might not know that they are upsetting or offending you or the rest of the group. For some people being late is cultural and expected. For others having technology on them all the time is just a sign of an always-connected populace. Try to work through the issues but if they are sucking the fun out of your hobby have them move along.
But never forget these are games. Let’s all have fun!