Let us now go over eight of the pitfalls players and Dungeon Masters alike can fall into without a chance to make a saving throw.
8) Putting Wayyy Too Much Money Into It
Wizards of the Coast wants you to buy books; doesn't mean you have to. Getting too much money invested into it tends to make one uh, poor, and unable to provide other things, like food or electric lighting for the game. Plus, when you buy extra supplements, Monster Manuals, you invariably feel the need to use them, which never ends well. Four times out of five players can't help but use these new rules to make ridiculously overpowered characters, like a half-elf half-minotaur paladin ninja (with druid magic!), making players jealous and the game less fun with your dominance. Plus, this which means the DM now has to learn all the nonsense about your new character which invariably slows the game down and makes all the other players hate you more. Really, the core rules can be all you need to have fun. You can make your own monsters. You can make your own neat pictures of those monsters. Also, you really don't need twenty pairs of dice. Seriously, nobody is that impressed with your gold-plated D20s. There is no bling in this.
7) A Terrible Location
You can, actually play D&D in a location that wrecks it. You need somewhere that has a large enough playing surface, comfortable seating, and no outside distractions. Not having one of these things can make things awful. Nobody wants to roll dice on a surface where there's a good chance of the dice coming off the table. Nobody wants to sit in a folding chair for five hours, trying to fight off back pain. Nobody also wants to compete with the noise of someone watching specific sporting activity in the next room. So, say, playing at a bar is not a good idea. Libraries, only if you have a private meeting room. Surprisingly gaming places typically have an adequate surface, but too may distractions and never any good seating.
6) Forcing It
You know, you can't bash through a door if you don't have the proper strength. You also can't have a good game if people aren't up for it. Yes, there is that fear that if you don't do the weekly scheduled game that people will suddenly stop doing it. A valid fear, but you also have to realize that some weeks just suck ass. Maybe someone got a large letter from the IRS. Someone's cat has cancer. Someone's hot horribly burned while they were trying to recreate the Mythbusters test about the hot water heater explosion. The real world can get focus so you can settle back into your fantasy world, and really, by allowing this to happen you can have happier human players.
It is one thing to play like your lawful good cleric hates the necromancer in the party, but it's another thing to have Marc hate Tim. Usually, this happens between good friends, who are both really into the game and really want to do well and find a simple disagreement between "charging into the abyss" and "checking for traps" leads for half the people to charge into the abyss and half the people checking for traps, and both being murdered by kobolds. Fortunately, people with really strong opinions that don't want to listen to others tend to stay out of adventures entirely and stick to DMing.
4) One Player Not Giving a Damn
It's fine to have an attitude towards the game like The Dude, not taking authority too seriously, endlessly searching for white Russians. You are there to have fun, after all. However, there are those times where people find it more fun to just mess with everyone else. These are the people who say "I backstab her!" to the Princess you just rescued, or "How many of them can I seduce?" to a room full of vicious Kobolds. The best thing you can do in this case is telling them to stop dating one of your friends or stick to the only Fantasy RPG with "Football" at the end.
3) One Player Giving Wayyy Too Much of a Damn
Rules are made to be broken, and in D&D well, the rules shouldn't really be broken, just not strictly adhered to for every... little... thing. The game is meant to be... a game, so it's meant to be fun, and if getting into fights over strict adherence to the rules is your thing, you should really just become a lawyer, because you are ruining for everyone. No really, calculating your moves down to the last footstep, taking in ability scores, encumbrance and wind direction to walk across a room and open a door is not...fun. Also, most of the time, your DM is just going to make fake rolls behind his DM screen anyway. You're likely to make everyone throw you out on your glasses, like Brainy Smurf.
Being too attached to a character is no good either. It is just words on paper, usually written in pencil or printed out. You can make another one. Your life doesn't end when it does. There's a whole world of characters besides the lawful good monk who can break people in half with her fists. There's a neutral evil fighter just waiting to enter your next adventure and cleave a few Orcs in half.
2) A Shitty DM
Dungeon Masters are god, so when Dungeon Masters suck, everything sucks. All the above problems are so much worse when the Dungeon Master has them. A DM who's spent too much on supplements often tries to cram them all into his/her campaign, which makes them an incoherent mess. Look, nobody ever says "That adventure was really entertaining because is was purchased and you included every elemental from the new Monster Manual." And when a Dungeon Master hates a player in real life, it's practically impossible to stay impartial when you have complete control over their character's life. A DM who cares waaayy too much and always puts the rules over fun and story, or feels the need to check every rule at every juncture basically turns two-hour adventures into 16 hours of math homework.
But the biggest problem a DM can have is what I call Bastardosity. It's like animosity, but with more dickishness in it. These DMs do nothing but try to kill characters and screw over players. Oh, there's a time and place for that, and certainly, a flair for occasional cruelty is definitely an asset for any gamemaster. But we all know these DMs who feel they're playing against the players, and the only way for them to "win" is when all the PCs are dead. A game where you never get to set out on the adventure because the tavernkeeper happens to be the brother of the lich-king you heard of 20 seconds ago and has poisoned all your drinks? That's Bastardosity.
1) Getting Older
This is horrible, but it is true: when you are a teenager, spending several days exploring the Forgotten Realms is a relatively easy thing to accomplish, as an adult, not so much. People as they age tend to get more (ugh) responsibilities and don't have the time to get five or so people together for a few hours a week. Things get in the way, like "children" and "jobs," and "gall bladder surgery." You can do it if your really, really want to, but like a wizard out of spells trying to beat down a Frost Giant with his bare hands, it's difficult. You may think retirement will free up the time to play Dungeons & Dragons but it gets pretty hard to read the small text in a big book after a while, and there isn't much fun making actual saving throws for heart attacks.