It’s been said somewhere that the act of walking is a series of controlled falls, you lean forward slightly, and catch yourself with an outstretched leg. That leg then propels your body forward as your other leg swings forward to catch you again and so on. By this example, it can be said that walking is not about not falling, but falling in a fashion that gets you to where you want to go.
GMing is a similar process. It’s been said time and again that GMs should know when to let go, when to allow things to go their own way, whether by the volition of the players or the vagaries of chance from a lucky (or unlucky) die roll. The key to running a game it not to prevent these unpredictable things from happening, but to learn how to hone them into a fashion that is ultimately entertaining and rewarding to all the participants in this activity.
I find it entertaining (and challenging) to take what happens in a game and swing them in a fashion that makes sense, and works out to be entertaining to everyone in the game. It’s not always easy… part of it is planning, another is profiling, and the last can be pure dumb luck. Still, the best advice I can offer newer GMs is to relax and go with the flow, and be confident in your ability to run a game. As long as your players are having fun, then there’s nothing wrong with your game.
Does this mean that I can’t sustain a plot though? Maybe, but then again, I tend to subscribe to the “… and life goes on” sort of deal. Player characters evolve, experience new things, grow old and continue their stories in a fashion that their Players choose when they’re retired from active play. What this allows me to do however, is to wrap things up at an interesting high note where the Players are happy, then put the campaign away, leaving it to the memories of those who played it.