Destiny isn't what it used to be.
Fate or Destiny was once written in the stars and spoken in prophecy. It was the will of the Gods, guiding mortals towards predetermined ends, no matter their opinion on the matter. Now, the gods are dead or their power shattered, and mortals are free to make their own way... But Fate, much diminished, remains.
In the world after the End, Fate is like a force of gravity that pulls things towards certain ends. It rearranges events in small, but far reaching, ways. The wood of a road sign rots and falls, leading a cart down the wrong road, and when its cargo of medicine never arrives, a village succumbs to the plague. A squall at sea delays a ship long enough for the pirates to seize it. An arrow destined to strike its prey is guided to hit true by an lucky gust of wind, and so it goes. Fate does not concern itself with good and evil, or even consequence, only fulfilling its own directives.
But with no gods to guide it, Fate is both easier to manifest and to foil. Fate is like a disease; something you acquire, which then spreads to every aspect of your life. The easiest way to become burdened by Destiny is through magic - Mages and mystical creature both have the ability to bend Fate and inflict it on enemies, or bless themselves or friends. Spells like Whims of Destiny
or Sever Fate's Threads
create or destroy Fates.
There are new limits to Fate's reach, too. Destiny was once only limited by competing gods and the servants they assigned to see it through. A strong will, a powerful effort, or an unexpected interference can call throw Fate's yoke off its intended victim... Or rob them of a boon they were supposed to enjoy. No matter how much a warrior might've been Fated to survive a battle will save them if a greater force put their mind to the opposite.
Places and objects can be Fated, too. A oasis can hold the Fate to save a king from thirst or to dry out when a nation need it the most, or an arrow Fated to slay a dragon. Just like with people, Fate's pull have grown feeble without the gods, and is more easily avoided... But it can still be enough to save, or damn, a person... Or a kingdom.