Einstein showed us that time is relative and can be affected by velocity and gravity.
Clocks in the basement run slower than clocks in the attic - this has been measured and proven already (the difference is in nanoseconds, but, the difference is important).
Moreover, the closer to the speed of light an object moves, the slower time moves for that object relative to everything else.
This proves that simply by passing by an object with immense gravity or moving at an extremely high velocity a human could pass through time at a slower rate than time on Earth, return to Earth and effectively have traveled into the future.
This is time travel without the use of exotic, science fiction-esque time machines, but just a natural happenstance of everyday reality.
If a person could use space-time in a circular way, effectively traveling backwards in time, it would raise certain obvious questions.
Could that person change the future?
Presumably that person could effect changes, but not in any way that would restrict that person from reaching the point in time from which he traveled to the past.
For example, he could not assassinate his own mother, because that would lead to a paradox. However, he would be able to prevent an assassination of his mother, leading to his own birth, and that would not lead to a paradox.

So, assuming that a person could naturally navigate into the past by means of manipulating space-time, what would stop that person from committing actions that lead to a paradox?
Essentially, what I'm asking, is this: does the universe have a mechanism that would restrict humans from causing paradoxes? If so, would that be what we commonly refer to as fate? Does this bring notions of fate and destiny out of the realm of the supernatural and into the realm of the natural?

Is it possible that all the things we consider to be supernatural simply be a category mistake due to our ignorance of the ultimate nature of reality?

"It's like you were meant to be a teacher."
"Maybe it's my destiny."
"Maybe...or, perhaps, if you don't become a teacher the universe will implode..."
"Perhaps."