Why are firefighters so friendly?

I live near a firehouse and the guys are so nice and friendly. They just somehow always receptive to people, greet people with a smile, give free firehouse tours (they never get tired of it by the way). Someone fell across the street from the fire station and they invited that person in for a coffee and gave him an ice bag for his injury.

I was just walking by as I glanced into the fire house and the dude swiveled his chair around to look at me. On the other hand, I hate people and find them to be problematic. I just can't imagine how on earth some can love people so much. I'm a nice kind person by the way. I'm not some cold heart grinch

Why are firefighters so friendly?
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