Mabon, the autumn equinox, is something of a blank slate. In the Wheel of the Year, the “cross-quarter days” are Celtic fire festivals; the other solar festivals - the solstices and the vernal equinox - are grounded in proto-Germanic cultures. In those Germanic cultures, though, the autumn equinox has no strong history of celebration; it doesn’t even have a distinguishing name. To keep the Wheel of the Year in balance, Gerald Gardner included the autumn equinox, but left most of the details open to interpretation. The name Mabon, drawn from Welsh mythology, came into common use later on, but doesn't do much to specify the nature of the festival.
As a result, different ways of interpreting the multiple harvest festivals have sprung up. Some groups focus on the Celtic roots of Lunasa and leave the harvest symbolism to Mabon; others describe Lunasa as the start of the harvest and the equinox as its end, and may call the festival Harvest Home instead.  Still others describe Lunasa as the grain harvest and Mabon as the fruit harvest. It depends on the group, and the bioregion, and the weather. This multiplicity of interpretations is one of the things I love about Paganism: each open space is fertile soil where multiple myths can take root and flourish simultaneously.
Understanding and relating to Pagan myths has taken practice, though. When I first became Pagan, I used to be confused and sometimes downright irritated when I read tales of deities who didn't seem very godlike, coming from a monotheistic perspective. I mean, they get drunk, they have fights, and they cheat on their spouses, not always in that order. They're not exactly the kind of example we'd want to imitate in most cases.
As I grew in my practice and engaged more with the myths and with different kinds of stories, I gradually reached the conclusion that my assumption - that myths are stories about gods whom humans should seek to emulate - was a holdover from my Christian past. In Christianity, religious narratives about Jesus or good Christians are presented as exemplars for followers to emulate. This approach is very god-centered, and when taken to its (il)logical extreme, it can almost erase the adherent by reducing her to a mere reflection of the beatified.
I’ve come to see the older myths as human-centric stories. The gods act like humans - and do they ever! - except that the gods are bigger and stronger, so when they screw up, they royally - or maybe deifically? - screw up. The myths reflect humans back to themselves, but enlarged. The stories don't minimize the bad in favor of the good, or vice versa; they magnify all the parts and possibilities, or they add unique features that weren’t present before.
The myths give both storyteller and audience the chance to engage with human stories in an exaggerated setting so that they're more interesting, more exciting, more dangerous, more tragic and more amazing. Throughout, though, they are fundamentally human stories.
This approach also helps me understand why so many overlapping, contradictory versions of the same myth can co-exist. The myths are no longer central; the teller and audience are, so it is natural for the people to adapt the myths to tell the stories they need to tell. No one is trying to find the single unchanging standard for behavior; the multiplicity of myths encourages us to adapt our responses to the situation, just as the storyteller working on the fly might have to alter the ending to fit the narrative corner she backs herself into. What matters is that the story works, that it's good enough, that it fits its context.
The most encouraging thing about this approach to the myths, though, is that because we're telling them, we can change them. They grow with us over time. And that's important, because my favorite myth is the myth of progress.
Historian Laurence Keeley, in his book on prehistoric warfare, wrote that modern people tend to view prehistory in terms of two competing myths: the myth of the golden age or the myth of progress.  The myth of the golden age conceives of the world as continually declining. It leads us to assume that the past was always better than the present - if not in hygiene or life expectancy, then in some in some ineffable but presumably more important characteristics like social structure and morality. The myth of progress supposes the polar opposite: it tells a story of continuous development, usually with technological and social development being used as evidence of the present's superiority.
It is quite accurate to describe both of these worldviews as myths; as the Slacktiverse's motto says, it's usually more complicated than that. Depending on the period and place that a historical narrative tries to describe, and what the narrative's author views as "good," it may seem that these myths take turns driving alternating ages of development and decay, or that one is predominant for all the period under consideration, or both, or neither.
For example, the history of Europe in the centuries after the end of the Roman Empire is usually told in accord with the myth of the golden age, while the history of the time around the Renaissance and the Enlightenment is usually presented as progress. Neither of these is entirely true or entirely false, especially depending on who and what the person telling the story considers important. Each framing, though, highlights some aspects and supports some conclusions, while pushing other matters into the background.
For the present moment, I try to make narratives that loosely fit with the myth of progress. I think that trying to tell our own stories as a part of the myth of the golden age is fundamentally discouraging, but trying to tell them as part of the myth of progress is a fundamentally optimistic position which can not only make us feel good but inspire us to do good.
To me, starting from a position that assumes the past was better seems like an invitation to despair; we can't get back there, after all, and if you think, as I do, that a certain amount of change is inevitable, then we may not even be able to hold on to the fragments of it we retain. The ability to learn and the ability to change are tied up together. An attitude of suspicion about all change seems to me to be inherently resistant to learning, and hence to growth.
The myth of progress, by contrast, is an invitation to hope. We can't change the past; we have to acknowledge it in all its beauty and grandeur, its cruelty and despair. But with that acknowledgement, we free ourselves to work on what we can change: the present, with an eye towards the future. As Terry Pratchett wrote, if we do a good job of changing our own present, when we get to the future, the present will "turn out to be a past worth having." 
In this way the myth of progress is more than an invitation to hopeful feelings: it is an invitation to hopeful action, to hope and love enacted. The myth of progress, and the mindset that comes with it, help me tell my stories in ways that guide my actions. Because I continue to have hope, I continue to put forth effort to make the world - and its stories - continue to improve.
And although some of the stories we tell are ones we really don't want to live through, sometimes we tell ourselves stories that we do want to live up to, stories that inspire us to be better than we thought we were. I think America's founders did that, for example, telling themselves a story about how things might work out much better in a society where religious liberty was guaranteed to all. The ones who found hope in that story were able to convince the ones who wanted to preserve an imaginary golden age of state-sponsored Christianity, and so there are clauses of the First Amendment to the Constitution which prohibit government establishment of a religion and guarantee free exercise to all.
But even at the time the Constitution was written, the story of free exercise for all religions was not the literal truth; it was in some ways a myth. Native Americans and slaves were not granted the rights the founders proposed, at least in part because they were seen as not really citizens and not fully human. State-sponsored Christian prayer continued in schools until the mid-20th century. Today, the US still lives up to that lofty ideal only imperfectly, but it has made tremendous strides towards making what was once a myth into a reality for more and more people. That gives me hope.
This is what I love about Mabon; more, perhaps, than any other Sabbat, it is a festival about which Pagans are actively making their own myths, in all their many forms. Mabon is an opportunity for us to look at our myths, and the stories we tell ourselves about our world, our past, and our potential futures. And since Mabon is so open to reinterpretation, it reminds us that if we don't like those stories, or where they're going, then maybe we can start telling the story differently, trying many versions, until we find the ones that we can live with and live in.
So, what's your myth? How do you use a myth - of progress, or something else - to tell your own stories?
 Here I use the modernized Irish spelling for this holiday rather than the "Lughnasadh" spelling most Pagans are used to seeing. ↩
 Keeley, Lawrence H. War Before Civilization. Oxford University Press, 1996, p 4-5.
 Pratchett, Terry. I Shall Wear Midnight. Harper Collins, 2010, p 336.
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