We are told that a person does not move his finger, unless it's decided in heaven, that that particular person, at that particular time will move his finger. So nothing is from us, and nothing comes from us. That begs the question - if it's all decided in Heaven, do we have to try and make an effort?
The answer is as follows. We do, but we still have to understand that it's not from us. We have to do what we know we have to do, but must understand that the fact that, for example, if I was looking for a job and someone gave me a job, the person who gave me a job is like the agent who was sent by הקדוש ברוך הוא, the Holy One blessed be He, to help me.
Of course I have to thank him, but the source, the ultimate source is הקדוש ברוך הוא, the Holy One blessed be He, because He is the one Who sent him to me. So we have to make our effort, but we have to understand, we have to always understand, that everything comes from Hashem.
The fact that I am successful - be it that I am financially successful, or famous, be it that I am good-looking, smart, or talented in a certain area - whatever it may be, it is all a gift that came to us from G-d. It's not from us, but all from Hashem. He brings certain people into our lives, so that we do what He wants us to do and so that what He wanted to happen will happen. It did not happen because we wanted it to happen, it happened because Hashem wanted it to happen. That is why He sent us certain people to help carry out the mission.
It is important to note that there is nothing wrong with trying for more. We have to try and do whatever we feel we can do. But we have to realize two key points:
1. That it's not us and
2. Whatever we get or don't get is a blessing from Hashem.
If, for example, we wanted to move to a bigger house and we succeeded in moving to a bigger house, then we must realize that it was not because we wanted to move to this house but because Hashem decided that that was what He wanted to give us.