"There are those who say fate is something beyond our command. That destiny is not our own, but I know better. Our fate lives within us, you only have to be brave enough to see it." ( Merida, Disney Pixar Brave)
I believe that fate has something to do with our lives but only in a small doses. i think that fate shows us possibilities of the future that could potentially happen, whether we act on it is a choice we make. Macbeth had a choice on to either act on what the Wyrd sisters said or just let it happen on its own. Shakespeare clearly also believes in fate has some part in your life, he uses "Divine Intervention" or the interjection of the supernatural beings to help push Macbeth forward.
obviously i could say that Macbeth and Banquo talking to the Wyrd sisters could be one example of Shakespeare using "fate" to determine your future However the use of the third murderer and Banquo's ghost are a much better representation of how fate plays a part in our lives. Firstly nobody tells Macbeth to kill Banquo but since it was an action that would "secure" his right to wear the crown, the use of the Murderer and Banquo's Ghost show that Macbeth is following the path that Fate has shown him. This shows that Macbeth also could chose his actions. So in a sense Macbeths future was both predestined but he also had a say in his actions. Shakespeare did that to give the play a sort of surrealism, so that the story line would stick around in the back of your mind.