In the chapter "Karma" of Wherever You Go, There You Are Jon Kabat-Zinn describes the concept of karma as "... the sum total of the person's direction in life and the tenor of the things that occur around that person, caused by antecedent conditions, actions, thoughts, feelings, sense impressions, desires. Karma is often wrongly confused with the notion of a fixed destiny. It is more like an accumulation of tendencies that can lock us into particular behavior patterns ...". He then suggests a way to open the door to free will:
Here's how mindfulness changes karma. When you sit, you are not allowing your impulses to translate into action. For the time being, at least, you are just watching them. Looking at them, you quickly see that all impulses in the mind arise and pass away, that they have a life of their own, that they are not you but just thinking, and that you do not have to be ruled by them. Not feeding or reacting to impulses, you come to understand their nature as thoughts directly. This process actually burns up destructive impulses in the fires of concentration and equanimity and non-doing. At the same time, creative insights and creative impulses are no long squeezed out so much by the more turbulent, destructive ones. They are nourished as they are perceived and held in awareness. Mindfulness can thereby refashion the links in the chain of actions and consequences, and in doing so it unchains us, frees us, and opens up new directions for us through the moments we call life. ...
Well, maybe that's "free will" in one sense of the term, or at least an escape from obsession. Later in that same chapter, Kabat-Zinn concludes:
If we hope to change our karma, it means we have to stop making those things happen that cloud mind and body and color our every action. It doesn't mean doing good deeds. It means knowing who you are and that you are not your karma, whatever it may be at this moment. It means aligning yourself with the way things actually are. It means seeing clearly.
Where to start? Why not with your own mind? After all, it is the instrument through which all your thoughts and feelings, impulses and perceptions are translated into actions in the world. When you stop outward activity for some time and practice being still, right there, in that moment, with that decision to sit, you are already breaking the flow of old karma and creating an entirely new and healthier karma. Herein lies the root of change, the turning point of a life lived.
The very act of stopping, or nurturing moments of non-doing, of simply watching, puts you on an entirely different footing vis-à-vis the future. How? Because it is only by being fully in this moment that any future moment might be one of greater understanding, clarity, and kindness, one less dominated by fear or hurt and more by dignity and acceptance. Only what happens now happens later. If there is no mindfulness of equanimity or compassion now, in the only time we ever have to contact it and nourish ourselves, how likely is it that it will magically appear later, under stress or duress?