Why does "chance" exist?

Chance is actually pretty beautiful if you think about it. If you flip an infinite amount of coins once, half of them will land on heads and half will land on tails. I think that's pretty cool, no?

The etymology of "chance" is actually pretty interesting, it comes from the Latin word for "to fall", or to deviate from something. But why does this happen? I believe all that happens has a reason, if you drop a ball gravity will pull it down for example. What is this gravity that causes a coin to flip heads and not tails?

There also exists the concept of "determinism" in which everything that has happened and will happened is, you guessed it, determined. But that leaves the question, who determined it?

  The laws of physics.

Chance is nothing more than us assigning a mathmatical value to our own unknowns. A woman about to give birth was once thought to be a 50-50 chance with respect to a boy or girl, until we learned how to tell well before that. Once we figure that out, chance in that situation was eliminated.

I am unconvinced that chance does exist. All that exists is human inability to calculate all probabilities effectively. 

Also determinism is explanation enough it needs no conscious actor. 

Somehow, missed this thread when first published. I reject determinism out of hand, I am solidly in the camp of free agency. I do believe random events occur, though I also will argue for their still having a cause. Stuff like a coin flip cannot be predicted exactly because there are too many variables out of our control, such as the force applied by the thumb, the coin mass, and, therefore, the speed of the flipping, but, most random is the added, utterly random motion of the forearm moving up as the flip by thumb force is applied, which adds to both other factors. If the coin is allowed to land on its own, add bouncing to the difficulties. Ambient conditions, humidity, temperature, particulate in the air... all cause variation that is also difficult/impossible to predict. Much of our lives are encounters with random events occurring. I'd say there are more random events than those planned, and even planned events do not always go as planned due to variables out of our control, and to expect that all variables were predetermined to occur in all instances is just too cute to believe.

Everything might be chance.

Chance or purpose are seemingly the two options.