The reason Din Djarin (Pedro Pascal), also known as the Mandalorian or Mando, wears his mask all the time is not just for protection. It is an integral part of the tribe he was raised by.
The Children of the Watch are a cult-like group of Mandalorians that follow the Way of the Mandalore, an ancient faith. Finding Mando as an orphan, the tribe raised him in their ways as a hunter, but an integral part of their belief is that they keep their helmet on at all times, allowing no human to see their identity.
Of course, if you've seen the first two seasons of "The Mandalorian," you will know Mando has had to break that rule in order to survive and complete his missions. Hence, when Mando returned to the tribe in "The Book of Boba Fett" episode five, they banish him for breaking their code.