This concept is critical to understanding many life situations.
For instance, imagine a divorced man who remarries and begins a new life. Now with greater maturity, he looks back and recognizes that his first marriage fell apart because of his temper. Yet he also sees divine intervention orchestrating the events that led to the breakup. Things happened in such a coordinated manner – Hashem was right there, controlling it all.
So is he responsible for the divorce or was it the will of Hashem? Is he accountable for his children being brought up in a broken home or was that part of Hashem’s plan?
The answer is both. One is the reason; the other is the cause. It was his lack of self-control that caused his marriage to fail and, as such, he is responsible for the results. At the same time, it was the will of Hashem that it should happen. This is what Hashem felt was best for him and for everyone else involved.
We mortals have very limited sight, but we need to broaden our perspective and recognize that while Hashem runs this world, we are still given free will and are responsible for the choices we make.