I think complaining about new stuff is part of some people's "process." Meaning they hate/complain, work through their frustration, and once they're quiet they

I think complaining about new stuff is part of some people's "process." Meaning they hate/complain, work through their frustration, and once they're quiet they're also happy. I think it is much more common than people realize, many just don't leave their comfort zones. There is a difference however between being internally frustrated and hating the [new thing] and being toxic to everyone else. Shows immaturity, and can often be mitigated by having a polite sit-down and discussing it. Reminds me of the expression: "You can only change yourself no one else." Which would have me consider what can I do as a coworker to help this new employee fit in and to generate less friction. Not because you caused it, but because you may have the power to mitigate it.