As a GM, it's never a good idea to leave your players alone for any length of time and have them continue player interaction.  You might wind up coming back to a game of Call of Cthulu. 

Player interactions are fun.  There's almost always a time where one player can exact revenge against another.

Sometimes the role of GM is more like being a conductor than anything else. Keeping things on the rails is hard, hard work.  Threats of bombs going off is sometimes required to keep the train rolling.

Sometimes the most frustrating thing about being a GM is not knowing if your players are making a joke, or if they really are clueless.

 The main function as a GM is to describe the world to the players interacting with it.  This includes describing things happening to the players, including any pain associated with that action.  Sometimes GMs take great pleasure in this aspect of the job…

 As a GM, in order to keep the game moving forward, you sometimes have to use executive power and override player freedom.  This will be met with resistance, and it’s a delicate balance to maintain.  The power can be used too much or abused, and that usually spells death for the game.  Throw the player a bone and give them the illusion of a savings throw.

And to translate the last frame: "Savings roll, Bitch!"

Some players don’t take well to threats or blackmail.  Even when you hold all the cards, players will sometimes still pull at the leash.  

 Sometimes GMs are the embodiment of evil.  We just tell ourselves it’s for the good of the game, to make it more believable, if we have trouble getting to sleep at night.

 Sometimes personal life will enter the game.  It’s best to keep that at a minimum, but as a GM it’s hard sometimes not to take the opportunity to make a point, both in game and in real life.  Pictures help.

 Most of the time players gloss over their character bios.  They usually jot down one or two lines of generic backstory and focus more on the here-and-now, then fill in their history as it’s convenient.  What’s fun is when a player totally blows off the bio and makes up some ridiculous back story.  Wedging it into the game repeatedly makes the game even more fun for both the GM and players.  Except for the player with the bad back story, that is.