Before we can answer this question we need to state clearly that the doctrine of God's plan does indeed means that everything that happens follows God's plan. God's plan had to embrace everything or the plan would not work. After all, even the littlest things-one person we just happened to meet, the patch of ice we just happened to slip on-can change our lives completely.
To some, this seems wrong. They cannot believe that God "wants" any terrible thing to happen. They would be right if "wants" means "enjoys" or "wants to happen again." Belief in God's plan, however, simply means that God has a reason, a good reason, for everything that happens.
Surely it makes more sense to believe that this is so-that God has a good reason for everything that happens. It makes no sense to believe that God made a world where the bad decisions of other people, or bad luck, can affect the destiny of those whom He loves.
Besides, isn't it obvious that we are formed by so many things we do not choose? No one chooses their parents, their birthday, and countless other events that form or direct them, both before and after their first real decisions. Surely, if we are not in control of such things, God is.
There is also positive evidence that everything that happens follows God's plan. We have already seen the evidence that God made the world. Now, let us look at how God did not make the world.
God did not make the world not knowing what would happen next. God knew what would happen next, and the day after that, and the day after that.. He knew what would have happened if He had made the world differently. Therefore, what He did make must have contained His plan for everything that has ever happened and ever will.
Of course, God's plan for everything was also His plan for everything that happens to each of us-and also our response. This was His way to give us a share in our creation, to let us become our own person, and still make sure that we become the people He wanted us to be.
At this point, we do well to take a look at certain things that help us to understand the idea that everything that happens follows God's plan:
1) Hard things lead to good things that could never have happened otherwise. Though faith says this is always the case, it can be seen happening in terms of:
the bad breaks that lead to good fortune,
the greater appreciation we gain when we overcome something difficult,
and the growth that so often comes through pain and other problems.
2) We are here, not for a good time, but rather to prepare for our eternal life with God. Actually, we are here, not to become the people that we will be with God, but rather the seeds of the people that we will be with God. These are seeds that God will complete at the moment of our death, raising us up to the full life of heaven. Only then will the "why" of many of our experiences come to light. In many cases, we will find that things we went through will help us to understand God as otherwise we would not.
3) We affect each other. In the short term, we are giving one another the experiences God wants each of us to have. In the long run, as one thing leads to another, and another, and another. we are helping our human family to become the family best suited to share God's life.