Free will is the exact opposite of destiny. I do not believe in destiny. Why? Because I choose to believe in free will. However, it is easier to understand free will by observing the opposite, the destiny.

Here is the world with destiny. God controls our fate to be like this. We have no choice but to accept them all. If you are poor, then you are destined to be poor. If you are ugly then it is you are. If you are stupid or one of the unlucky, then you will always be like that. Every time you face a difficult situation or bad situation, you will see it as God's will and you just accept it. If a thief enter your house and steal from you, you will do nothing because you accept it as destiny. If there is an accident, the government will do nothing to prevent it happen because they believe it is just their fate to have those accident.
Suppose we take example of an accident that have victimize one of your beloved one.
If you trust the accident is just a destiny, then your trust will comfort you at once because you can accept it as unavoidable. Since it is inescapable, nothing you can do and the best way you can do is just to accept it as it is. What a great relieve. On the other side if you do not believe that the accident is a fate, the grief of that accident may consume you emotionally.

If you believe in destiny then you will argue that though we can do something to prevent that accident happen, whatever we do, it will be just a useless and waste of time because bad things will happen anyway. On the other hand, if you do not believe in destiny, this is the way of your thinking: While it is true you can do nothing when a bad things happen, it is not true that it is a fate that unavoidable. We can always do something to prevent bad things to happen. We can always prepare for the bad situation. Did you see the point now? Having faith in destiny make your way of thinking always comes from a negative point of view. You will always feel any effort is useless and it is better if nothing to be done. You point of view is desperate point of view. Conversely believing that you have a free will lead you to positive way of thinking, to construct, to improve, to prevent bad things happen. As the result in the long run, the community who believe in destiny will have no development while the society who believe in a free will have much more progress. You can only see the result in the long run, in the short time, however, believing in destiny offer comfort to heal the hurt.

Both theories of free will and destiny have been evolved to adjust to many different situations. The destiny believers now add that they believe in destiny but they never sure if it is their destiny or not, thus they will pretend it is not their destiny and do more effort to prevent the bad things. The free will believers now learning to accept the current situation as it is since nothing do can do except to prevent the next similar problem. Then using your free will to choose the acceptance of your situation, you will get comfort. Thus both theories seem to achieve agreement to compromise in the middle.

Why do I still insist to believe in Free will instead of destiny? Because you need a basis to begin your believe and I choose the Free will because the path is from the positive point view, while the destiny is starting from negative point of view. This decision to choose the free will influences very much my way of thinking.

Having a free will mean we determine our own fate. If something goes wrong, it is our own fault. If something goes better, it is our success. We don't blame any other person or situation or God or even Satan for our own failure and mistake. Failure is not always related to mistake or sin. Sin and mistake may lead to failure but not conversely. Random chance happens.