As stated previously, I believe that plot should be driven by what characters do. It is always best when stories are propelled by the decisions that characters must make, followed by those actions that they take because of those decisions, and all of the consequences that follow as a result. Decision making by a protagonist, regardless of whether he initiates the action or is reacting to one thing or another, should lead inevitably to the next thing that happens to him. This will cause yet another decision to be made, which will lead to another action, and so on.
