Keeping track of characters and events is the easy part. Having them do what you want is even easier. It's kind of like a perfect world. Everything goes the way you want. Then there arrives a point in which you're almost 'forced' into making a decision you had not intended. But then again, it's surprisingly fun.
A good story usually has parts to it that you don't like because the course events may take that leave you telepathically screaming 'NOOOOOOOOOOOOOOOOO!' That makes a story more believable because it mirrors life in that 'the cookie doesn't always crumble the way you want it'. While we all want everything to go well, the good guy to win, and for the world in our stories to go on as perfectly and smooth as it could be, that would be incredibly dull and boring. Adversity adds flavor, creating interest which lures in those who may wonder: What happens next? That one little thought generates curiousity which is satisfied by exploring the story, usually from beginning to end.
Another facet of that little wrench in the works, adversity, is the antagonist. Everyone loves to love the bad guy. Some may be utterly evil, invoking a shudder of extreme revulsion at their very being. Others are masked beneath a thin veil of smiles, popularity, approval, and good intentions. Others still have become the bad guy, usually through a series of unfortunate events. But they all have one thing in common: they're fun to write, usually more than the hero. I love to write them, particularly when trying to write the baddest of them all. I look at it like Alexander the Great on his deathbed naming a successor from among his generals: Kratisto, To the strongest.