There are many wonderful things about being a Game Master, but I think it's fair to say both that filling that role takes practice and that we can make some silly errors while learning. Thinking back to how I GMed before beginning Pathfinder Society Organized Play, I realize that many of the tricks I pulled on my players were downright cruel, such as heaving colonies of rust monsters at the fighter, swarming the bard with wererats until he was infected and under GM control, repeatedly giving one player an intelligent greatsword that would inevitably betray him, having a creature "adopt" the party wizard in a familiar-master bond just so I could kill the familiar and drain the character's Constitution score, and repeatedly tempting the characters to betray the other PCs for power and wealth. Yep, those were some really bad campaigns (yet everyone kept expecting me to be the GM), and I think it's telling that I can remember little of their overarching plotlines. What I can remember, though, are the villains.