Processes of becoming can operate simultaneously on many levels, both short-term and long. The fact of your being a human being in this human world is a becoming that resulted from a desire that appeared in the mind as you were leaving your last lifetime. Within this larger becoming there are many shorter-term becomings that coalesce around particular desires related to possibilities in the physical world. There are also many more fleeting becomings that are purely mental, as when you conceive a desire to think and take on the role of the thinker thinking the thought, or of an actor in the world of your thought. These levels of becoming are interrelated in that physical levels of becoming can inspire mental ones, and purely mental becomings can form the seed for becomings on the level of the physical world for short periods of time or for entire lifetimes.
The process of becoming is related to the issue of suffering and stress because any desire leading to becoming is also a cause of stress. To gain freedom from stress requires putting an end to all desires leading to becoming. The Buddha identified these desires as falling into three categories. The first two are intuitive: sensual desire and desire for becoming itself. The third—the desire to put an end to any existing becoming—is counterintuitive but it can be explained in that any action to destroy a becoming requires taking on an identity built around the desire to see it destroyed. This in turn forms the seed for a new becoming.
This reflection by Ajahn Geoff is from the book, Beyond all Directions, pp. 81-82.