I read somewhere scientists ran experiments on hypnotizable subjects and observed their reactions when they made them think of only, in turns, the past, the present, and finally the future. Don't ask me how they could do that, but anyway;
when only in the past, they were sad and morose;
when only in their present they were all business, pragmatic, focused;
when only in the future they were giddy and thoroughly, unreasonably elated.
If true, sounds like living in the past is not a good place to be.
I think everybody judges everybody else all the time. It's automatic. How could you stop yourself from doing so, even if you could?
If you mean, judging others with unfair harshness while thinking yourself perfect? Would that make that person unhappy? I don't know. Maybe, maybe not!

True! We could turn that truth on his head and say happiness is living in the moment..

Yup

Past is very useful . Appreciating present is vital . Looking Frwd to future is a good idea . Judging everything , self including , is skillful . Contempt everyone and anything just Bcz not your cup of tea , is stupid .

Truisms are sophomoric at best. Sure it's true, but there's several volumes of codicils that need attached.

I have alot more respect for self reflection and complicated emotions. Happiness as a goal seems very shallow in the American sense at least.

Judging others can be a great source of satisfaction. It depends on what you judge them for.

If one lives by past negative experience, then assumptions about the present might be negative. To judge others incorrectly, one is likely to presume to know more about them than one actually does know.

The past is memories. Without memories, you have had no life. No thanks. Judging others is fun and necessary. Life is constantly judging others. It is the way you keep from getting sucked in, fucked over, or worse. No thanks again.