There is as much difference between us and ourselves as between us and others. -Michel de Montaigne, essayist (1533-1592)Montaigne wrote a lot about recognizing the differences among people, but this quote suggests he also understood that we ourselves do not maintain a single "self" over our lifetimes.
In GS readings, you might encounter the term RIOT, standing for Relative Invariance Over Time. This concept accounts for our ability to simultaneously recognize ourselves in baby pictures and in the mirror, despite the years between the two images. GS considers our "selves" to represent a different level of abstraction than our bodies at any given moment. RIOT represents a chain of evidence, if you will, that links that child to this adult, a chain we can grasp conceptually as a single entity due to our skill at categorization.
But while that gives us the ability to carry on from day to day and still pay the bills and visit the in-laws, we do well to retain an awareness of the underlying, less continuous, less consistent, less conceptual being that changes minute by minute and hour by hour. While the *concept* of "I" recurs every day as the "same person", the *fact* of "I" changes--we age, we fall ill, we learn a new skill, we forget an old friend. We think one thing one day and a different thing another day. We find ourselves unable to decide something because we can see both sides, or all sides, and part of us wants one thing and part wants another. We differ from ourselves.
That covers the first part of Montaigne's quote.
As for the second part, we face similar but different issues. RIOT accounts for our ability to recognize others as a) humans like us; and b) strangers or acquaintances. We can easily grasp the benefits of RIOT here--we can operate in our society without continually have to retest our perceptions of those around us.
On the other hand, when we do not retest our perceptions of those around us, we fail to detect changes that might have significance for our interactions with them. We do not notice that we may not agree on how to conduct civil discourse, how to govern, how to share resources, etc. Overlooking disagreements about how to do something in a shared environment usually leads to discord, disharmony, divorce, even war. After all, while we are overlooking differences, so are the other folks, and who decides which side of the difference "is right"?
More than anything, Montaigne wanted to encourage us to recognize that no "right" exists, to recognize that we do things the way we do them because we learned to from our ancestors, who learned from their ancestors. We revere our ancestors because they produced us and told us what to hold true to, but we have no basis for saying that what they taught us has any independent validity. And the other guys have just as many ancestors with just as many beliefs, equally without independent validity, but still cherished as true. So we differ from others too.
So, without thinking about this, we war amongst ourselves and we war within ourselves.
Can understanding the mechanisms for these wars help us avoid them? Perhaps, if we incorporate that awareness into our deliberations, if we account for both the RIOT and the changes it obscures, both within our selves and between us and others. If we know we cannot require ourselves or others to remain unchanged, if we accept that what we know and what we learned may not match up with what others know and learn, if we grant ourselves and others the leeway to change and differ, we have taken steps closer to a saner, more accurate map, and that seems like a good way to find our way.