Fate will happen in the future, usually because of a choice you made, or someone else did. Fate is like the lines that connect the act of cause and effect. These fates make up many branching paths in our experiences and can change by the slightest change in our choices. Fate can be chosen if one can see where they are supposed to choose. Fate can be quite predictable at times and can even be seen through divination tools, but fate has a very unpredictable nature because of how easily it can be changed. From what I understand, readings show the fate of the future from the point in which an individual is presently at, and it has the likelihood to change based upon different variables set forth by will. Simply by just knowing your future or getting the reading in the first place can change your fate due to the fact that you have introduced a new variable into the working that an individual would be able to use to influence their will. So choosing to do something different or changing something even very slightly can have very interesting and expansive effects on the future and can result in you being pushed down new paths of fate. Simply doing divination for a situation can allow that situation to change as long as that information impacts the will of an individual who is, will, or would have interacted with such a situation. Readings can show you the path you are headed, but it is your choice and the choice of the things around you that determine if you walk that path. This makes these fates very volatile and uncontrollable at times, depending on our choices and the choices of the world.
Destiny will happen in the future regardless of anything you do or anyone else does. Destiny is out of your control and cannot be changed. It is written in stone, and whatever is supposed to happen will happen one way or another. This is different from fate because it is more like a fate that one would not be able to avoid, So destiny is just a hardcore version of fate.
Everything in existence has a causal chain where all causes and effects lead to each other. The line that will be traveled is Destiny and it in itself is a fate, but along with Destiny there are other perceived fates that it looks as if an individual could have chosen.