"One should never deviate from the customs of the place he visits."
This quote is from:
a) Lonely Planet (popular travel guide)
b) American Airlines commercial.
c) Charles Veley (self-proclaimed "world's most traveled man"—the youngest recorded person to visit all countries of the world)
The correct answer is:
d) None of the above.
This equivalent of "When in Rome do as the Romans do" is actually a Jewish teaching, quoted in some of the foremost sources of Jewish wisdom: The Zohar,1 Talmud,2 and Midrash.3
But isn't the idea of conformity completely out of character, if not antithetical, to Judaism, a religion whose Book and People distinguish themselves by their ability to fight ignoble ideas and practices prevailing throughout history, no matter the circumstance or consequence? Were not G‑d's people chosen to be the salmon that swims upstream?
Imagine if we had "never deviated from the customs of the places we visited" since our inception and throughout our drawn-out exile; we would long have assimilated into oblivion…
But as we shall see, the seemingly puzzling statement teaches a profound lesson about transforming, rather than advocate for conforming.
A Remake
Reading the Bible, one is struck by the fact that its most monumental event, the Sinaic Revelation and accompanying Ten Commandments, turn up twice; first in Exodus and then in Deuteronomy.
(Don't panic, same ten.)
If the event happened once, why tell it twice?
The mystics explain: While the Torah was given once, it was received twice, or in two phases.
There was something very powerful about the Divine revelation at Sinai. Too powerful, in fact. We, the world and its inhabitants, were overwhelmed by G‑d. At the time, all physical properties were out of order and sync, neutralized by occupying Divine forces.
No doubt it felt good, as we ascended and transcended time, space and body. At that spiritual altitude and aptitude, G‑d's existence was unequivocal and concrete; it was actually material existence that suddenly came into question. We were high on a spiritual drug, experiencing a state of altered reality.
At Sinai, the Jewish people "saw that which is usually heard and heard that which is usually seen." The material world was under general anesthesia, unconscious as the Almighty operated.
But then we woke up, bruised and hurting. The experience had been too intense.
Indeed, the story of our people's challenging desert travels bears testimony to that trauma. We were simply reacting to too much exposure. Our spiritual senses were dulled by being overly stimulated during that deeply personal and meaningful conversation with G‑d at Sinai.
(Does this offer insight into the enigmatic behavior of the Jews who sinned so terribly and consistently soon after experiencing lofty revelations?)
When our souls returned from their spirit-fest to our human faculties, the real work of internalization and integration began. Day-to-day existence resumed and with it the need for dialogue between body and soul.
That healing process would take decades, with Moses serving as physician. Throughout his tenure as their leader he would work hard to nurture their faith as well as provide them with soul/body equilibrium.
Which leads us to the second account of the Ten Commandments in Deuteronomy; less glamorous, but (therefore) more sustainable.
On this occasion, forty years after receiving the Ten Commandments straight from G‑d, the Jewish people heard the Ten Commandments again, but this time as they were processed by Moses, a human being (somewhat) like them. It was there and then that the purpose of Sinai was realized, for at that juncture in Jewish history, G‑d's will and wisdom, which in their raw and undeveloped form overbear all things physical, had successfully learned not to "deviate from the customs of the (physical) place it had visited.4
What's in It for Me?
In one form or another, many of us seek to influence, give and share with others. At times we feel like we're giving our all, but getting no response, or worse.
As any parent can attest, the most difficult acts of love for their children are the ones which demand holding back, for it's unnatural for a lover to withhold anything from their beloved.
But since when is true loving natural?

Good Q Hi Lee,
First of all, thank you for your kind words (to Anonymous and Benny as well).
As for your question: The deeper meaning, or message, of the saying "One should not deviate from the customs of the land" refers to the need for tempering or tailoring spirituality when it encounters the physical. As the former comes from "a different land," so to speak, than the physical (with different frames of reference, perspectives, value-systems, properties, etc. -- they "speak different languages"), it is important to appreciate the limitations of the material mindset and adjust the intensity of the spiritual encounter accordingly. Ultimately, this is how the marriage between physical and spiritual is best sustained.
I hope this helps,