When I finally got a job that allowed me enough money to play Dungeons and Dragons, and was settled in an area long enough for it, I went to the local hobby shop and bought the core rulebook for Pathfinder. It had been described to me as Dungeons and Dragons 3.75 and I was curious and interested after having lurked the internet on it. I was blown away, and quickly found myself buying the splat books that were put out to go with it, my next step was to run a game, however. This led to me discovering that, even if you have a good storyline laid out, every single player is a spanner in the works, and does what he or she wants to.
For example, in the very first mission, instead of fighting the kobolds like I expected them to, they decided to sit in the inn and drink grog. I had to coax them out of the place with goblin tagalongs throwing firebombs through the windows. The townspeople, of course, thought they were heroes, if anything they should've been hunted down by a group of paladins for their rather dark methods. That and the fact the party had some sort of undead homebrew, a goblin, and at least two half orcs. I have nothing against half orcs, but the other two draw a little more attention.
A baby got stolen by the kobolds, and the party had to be paid a fair amount of coin to rescue it, and by a fair amount I mean an obscene amount. Somehow, they almost had a TPK in the first part of their infiltration into the kobold lair, and an NPC had to rescue them. It would've been a TPK if one player hadn't decided to run away. See what I mean by spanner in the works? They all just ran in like Leroy Jenkins, minus the shouting. Then, if that wasn't bad enough, they shot a flaming arrow into the cave opening, and only after they saw fire did they remember a baby was in their. While their reactions were hilarious, they did not actually kill the baby. They did, however, end up throwing it like a football to escape from a green dragon intent on keeping the babe as a replacement for it's slain offspring. The dragon wound up taking the baby back from the town, but the burning town didn't matter to the group walking off to their next adventure.