The Mandalorian series has done a pretty thorough job explaining why
It seems as if all of his positive qualities have been forgotten the moment he took off his helmet. According to The Way, Mandalorians are not allowed to remove their helmets. If another being sees a Mandalorian warrior without their helmet, they're forbidden from ever donning it again.
Mandalorians are just not allowed to take off their helmet in front of someone else. No other being can see their face. It's totally fine to take off the helmet in an isolated environment though. So what happens if a Mandalorian shows their face to another person?
When Has the Mandalorian Taken Off His Helmet? The Mandalorian has taken off his helmet three times on the show. First, he takes it off in the season one finale, when the droid IG-11 treats him after he's badly injured.
“It's like putting on a head-to-toe glove with weights on it,” Pedro Pascal tells Empire of what it's like being inside Din Djarin's Beskar get-up. While that helmet is impenetrable for his enemies to see beneath, it's equally as difficult for the Mandalorian actors to see out of.
How do Mandalorians shower? Bounty hunting is a dirty business, and it's unlikely that basic hygiene is off the table for the Mandalorian, tradition notwithstanding. While this hasn't been confirmed outright, we can also presume that Mandalorians also shower or bathe in private, sans helmet.
Religious Mandalorians like Din Djarin prove their devotion to the creed by never removing their helmets. And native Mandalorians are the ones you see removing their helmets. And that's not to say native Mandalorians can't also keep the creed.
And while there are many rules guiding Mandalorians and showing them “the Way,” the most iconic aspect of their culture is related to their armor. That's because, as Season 1 of The Mandalorian underlines, true Mandalorians are forbidden from ever taking their helmets in front of others.
Clone Wars
Notably, the Dagoyan Masters of Bardotta regarded the Jedi as thieves and kidnappers because of that practice. Some Mandalorians, most notably members of Death Watch, held a grudge against the Jedi for their perceived crimes against Mandalore during the Mandalorian-Jedi War.
While most of them are humans, there are also Mandalorians of various other species. Mandalore serves as the Mandalorians' home planet. It was originally inhabited by the Taung species, who renamed themselves Mandalorian and created the culture practiced by later non-Taung Mandalorians.
Every since the series debuted and confirmed that Mandalorians never remove their helmets, I've been wondering how they get any sort of nutrition. The answer, it turns out, is neither “through a secret hole somewhere” or “they exist on a liquid diet” but rather…they just eat in private.
He was a foundling who joined the Mandalorian Creed and never took his helmet off after wearing it. According to the ancient way of Mandalore, a Mandalorian cannot remove his/her helmet in front of another living being. If he/she does that, then they will no longer be a Mandalorian.
Mandalorians do marry and can marry anyone they want.
The rule is that he can't remove his helmet in front of any living thing—which means he can remove his helmet when he's alone or even in the presence of a droid (since droids aren't technically alive).
Though Mandalorians were usually distinctly human, one did not need to be human to become one. Instead, what one needed to do was follow the Mandalorian Creed. Thus, some individuals, non-humans included, could be adopted into the Mandalorian creed as foundlings, children raised to become Mandalorian warriors.
Mandalorians' weddings are simple, and they can marry anyone. If they wed a non-Mandalorian, their spouse needs to vow to live by the ways of Mandalorian society to join effectively. Queer couples were allowed to marry as well.
Bo-Katan dismisses Boba as a pretender and a disgrace to his armor, refusing to acknowledge Jango Fett as the father of Boba and disparaging him for being a clone.
Re: Question - Why can't mandos use sabers? Dha pretty much nailed it. Mandalorians and Jedi just don't get along, and as an almost universal rule Mandalorians reject using lightsabers.
Ultimately, it was Vader who took the Emperor down, a move that ultimately destroyed the Empire. Darth Vader is a large, imposing figure whose skill with the Force in combat makes him a fierce adversary. This is not a fight Mando is going to win.
By this logic, it's likely that Mandalorians are also able to remove their helmets for sleep as well. Since Mando felt comfortable enough to unburden himself of his headgear when eating, there's a good chance that he is fine with leaving it off when he is isolated from others while taking a snooze.
Is Grogu Yoda? According to the events of "The Mandalorian" so far, Grogu and Yoda are not the same character. They are simply from the same species.
To Din, "This Is the Way" embodies what it means to be a Mandalorian, and it includes a code of traditions and ideals they all must uphold.
In the Star Wars prequels, Jango removes his helmet more or less whenever he's not fighting, happy for Obi-Wan, the people of Kamino, Count Dooku and others to see his (or, indeed, Temuera Morrison's) face.
He has the darksaber
Din is in possession of the Darksaber, the weapon forged by the first and only Mandalorian Jedi, Tarre Vizsla. Tarre Vizsla is the only known force sensitive Mandalorian, and of course, plenty of people think Grogu is the next.
When we first met Mando on the ice planet Pagodon, he paid extra for a human landspeeder pilot because he refused to ride with a droid at the controls. It was later revealed in season 1 that Din's disdain for droids came from the fact that his parents were killed by Separatist battle droids during the Clone Wars.