Believing an assumption is a choice, though if I am unaware that my mind is filling in gaps, then this is not really a choice at all. I am at the mercy of my assumptions. But when I have that awareness, an assumption allows me to consider a possibility that will only become true the moment, and only at that moment, when it comes to fruition. If the assumption is incorrect, with awareness I am able to simply release it, and new possibilities abound. Seeing our attachments for what they are allows us to see that an assumption is merely one possibility.