The subject of fate comes up a lot in Empty Sky. Fate is a subject I've wrestled with since I first started reading fantasy novels, and I often find the way it's portrayed to be frustrating. I don't agree with the idea that we're bound in any unchangeable way. Free will and choice are important.
And yet... I've certainly been in situations where I felt like I was at the whim of a fate beyond my control. Patti-like relationships coalesced out of nothing, I fall comfortably into the same roles in relation to the same kinds of people, certain opportunities turned up out of nowhere and click into place seamlessly. It sure felt like fate. But as I recognized that some of those relationships, and a lot of those roles, were unhealthy for me, I understood that being bound to that "fate" was intolerable and I went looking for a way out.
I discussed this briefly in the article on blankness, but essentially, our past lives stack up behind us as we go. The vast majority of people are unaware of their past lives, and this is how it's meant to be, because the lives themselves have a sort of gravity. Important or pivotal things we've done in the past create patterns and echoes, and if we have not made peace with those actions, people tend to re-enact them. This creates a sense of fate, and is widely used in epic poetry and stories for dramatic purposes- the loves reunited! The lovers re-enact their terrible fate and nothing they do can stop it! A patti comes together in recognition, only to fall apart and perhaps die tragically! Two brothers realize they are the reincarnations of great generals who opposed each other! You can guess how that will end! Usually the characters recognize what's going on on some level, maybe even try to change it, but they ultimately end up giving in to their "fates" because the immediate desire overrides that awareness of a "bad fate." In short, fate is what happens when you're not paying attention.
This kind of fate can be short-circuited quite easily with free will - there's only habit drawing you into the same destructive patterns over and over again. Of course, you have to recognize the pattern, and you have to want to step out of it. Like riverbeds worn into valleys, it's easier to follow the pattern than to climb out of the grooves. But if can be done and it requires only effort, no magic or complicated rituals.
Any sort of magic or situation that pulls your past lives toward the "surface" and into the present can be fate-effecting. This especially comes into play with eclectic mages who intentionally draw out their past lives to learn from them, but can come up in other ways as well, most notably if someone runs into another person they share a strong history or patti membership with of if they find themselves in a situation that was pivotal for them in a past life. When past lives hang around, they bring their patterns with them, and the gravity of that valley is increased.
Figuring out how fate works has been a long-term project and is ongoing. Some people seem to have an over-abundance of fate, and when I'm writing them, they're clearly barreling toward an inescapable conclusion (usually a bad one). Others are blank, or might as well be. Most people are somewhere in the middle, getting stuck in the occasional pattern until life jars them loose with something unexpected.
The biggest challenge as a writer was to put aside my assumptions about how fate worked, most of which came from reading too many fantasy novels as a teenager, and instead draw on what I saw the characters doing and what my own experience told me. It's easy to assume we know how any given concept works, but that can limit the stories you tell by making them conform to genre convention instead of allowing them to do something different and exciting.