Karma, or "action," is a way of understanding the world in its entirety and that everything does indeed happen for a reason. Every story has cause and every consequence is an outcome that can be understood and determined.
Karma can be incredibly complex because all the variables that cause a particular consequence or outcome to occur is full of complexities. Karma can become difficult to fathom: not because we don’t understand the reasons for things but because there might be too many reasons or too much going on. In essence, karma is an accountability of sorts, the assumption is that everything does indeed happen for a reason and there is indeed accountability.
The ancient yogis understood the world as karma. The world was actions that could be understood as meaningful precisely because they can be tracked, they can be mapped, they can be accounted for.
But then we have the yogic term daivya, referring to destiny. Destiny is filled with divinity, made of god-like nectar. The gods know that everything that is, is the outcome of what has been, and that everything that will be is a predictive possibility that comes from the choices that we are invariably going to make.
The gods know which directions, choices and karmas we’re going to take in advance because they can see that trajectory. Generally, the gods don’t intervene with your karma, so destiny doesn’t refer to intervention by the gods or the gods making choices for you. Karma chooses that and the gods know what kind of choices you’re bound to make.
It’s as if everyone ends up doing exactly what they were always going to do. So destiny is: this was going to happen because of the constellation of karmas and trajectories that were always going to add up to this outcome. In yogic thought, destiny is already written in, but what’s still open for interpretation and a sense of free will for our lives, is that we get to decide what the meaning is behind all of it. In that sense, we can control less and surrender more.