It's a rhetorical battle between free will and destiny. A tradeoff if you will. They share
a pool of potential energy, meaning that the cost of more of one of them is the other. To put it more simply, an abundance of free will leads to a lack of inevitability (destiny's influence) while inevitability implies a lack of free will. Concordantly, if what we perceive to be our free will (i.e., ability to make decisions) is merely an illusion and isn't genuinely there, then destiny exists in the sense that all events that happen were inevitable.
Thus, an important issue is whether or not free will is, at least in part, an illusion. Let's see... Do you have free will to disagree with me?
Visions can be acted upon in a way that invalidates the vision. For example, person A has a (alleged) precognitive event in which s/he observes person B getting into a car wreck in a white car. Person B can then choose to never enter a white car and Person B lives happily ever after, invalidating the vision. If everyone and everything has a fate then visions aren't an ironclad method of discerning what fate will be.
That of course brings us to the dichotomy of natural future versus altered future. The natural future is what will happen if the status quo's inertia is allowed to play out while the altered future is when the status quo's "velocity" is altered. For example, consider that vision. The natural future for person B was to die in a car wreck in a white car. The altered future for person B was to not die in a white car because person B decides to never enter a white car. The existence of fate is equivalent to the existence of the dichotomy.
In other words, there is such a thing as an altered future if and only if not all things are destined to be. I believe that it is abundantly evident that altered futures exist at all times. By that rationale, not all things are destined to be. Some things are inevitable but not everything is inevitable.
And now for a quote from Matrix Reloaded:
This conversation is about a vision Neo had of Trinity's death.
The Oracle: Do you see her die?
The Oracle: You have the sight now, Neo. You are looking at the world without time.
Neo: Then why can't I see what happens to her?
The Oracle: We can never see past the choices we don't understand.
Neo: Are you saying I have to choose whether Trinity lives or dies?
The Oracle: No, you've already made the choice. Now you have to understand it.
Neo: No. I can't do that. I won't.
The Oracle: Well, you have to.
The Oracle: Because you're the One.
Let's not forget about causality. If causality is a real phenomena, then the effects of the causes are inevitable. However, not all events are caused; some are uncaused. The existence of uncaused events is equivalent (i.e., equally true or false) to the existence of that which isn't inevitable (i.e., not all things that happen were destined to happen). Reality's existence is an uncaused event, establishing that there is at least one uncaused event which implies, then, that there exists something which is not inevitable. Another word for an uncaused event is random. The existence of randomness flies in the face of the inevitability of all things (destiny). And randomness can be defined and shown to exist both physically (think quanta) and mathematically (think incompressible strings and Kolmogorov complexity).