I've recently been working with the ox herding pictures in my zen practice. For those not familiar, the ox herding pictures depict a developmental model of practice and stages through which a person passes on their way to enlightenment. The pictures describe progress generally and capability within specific aspects of practice, like meditation, specifically, and in using them to guide my own practice I've been reminded of an idea from my study of developmental psychology that I live with but not written much about—the leading and trailing edges of development.
The name gives away most of the idea, but for the sake of clarity I'll describe it in some more detail. If we assume a developmental model of human psychology (like the ones of Kegan, Commons, me, Beck & Cowan, and others) or even just a positive psychology model (e.g. growth mindset, positive disintegration, etc.) and permit that development doesn't happen evenly (a person may be more developed in some ways than others), then we can talk about the leading and trailing edges of development as referring to those aspects of a person that are most and least developed in terms of any particular model. I'll make this concrete with some personal examples.
I had an awakening experience a few years ago that I interpret as tipping me between predominately systems-relations thinking (Kegan 4) and predominately holonic thinking (Kegan 5). That said this was only true of my leading edge in aspects of my life related to things like my work in philosophy and organizational development. My trailing edge, by comparison, remained possibly as far back as thing-level thinking (Kegan 2) when it came to things related to, for example, romantic relationships. Now my leading edge gave me tools that helped me pull forward my trailing edge, but that was work I had to do and did not happen automatically, so knowing about my trailing edge helped me know where to work to catch up certain aspects of myself to be closer to the leading edge.
In my zen practice I similarly notice that, in some ways I express things you might associate with the 9th or 10th ox herding picture, like my general equanimity, surrender to the perfection of existence, and acceptance of emptiness, but in other ways I lag behind because I have a sense of self of the sort you might associate more with the 6th or 7th picture and my meditation practice could be said to look more like the 4th picture with me actively moving towards the 5th. And occasionally I discover things about myself where I seem to have not even seen the ox yet (2nd picture) where I run out of patience for something or experience anger or resentment. This suggests my leading edge might be somewhere around the 9th picture but my trailing edge might be as far back as the 2nd picture, with the large distance is likely due to my converging on zen teachings from a different direction initially.
The leading and trailing edges and the distance between them serve a few useful purposes in understanding developmental models of psychology. For one they highlight for a person attempting personal development that the path is not even and give you a way to talk about your own unevenness and accept your weaknesses and work on them without feeling guilt for not being more even. They also help us make sense of the way others may seem particularly mature in some ways and immature in others (you can point your own fingers at your favorite rationalist celebrities and other people from your own life). And the leading and trailing edge addresses one of the most common objections to developmental models, namely that people exhibit behaviours outside their assessed stage (stage essentialism is a strawman among modern developmental models, but the argument against developmental psychology based on it persists).
If you have other ways the idea is useful to you I'd love to hear about it in the comments!