I'd say I've witnessed it in others. Not to assume I could speak for them but, put it this way, they described life as 'precious'. Did everything go right in their life? Not by any means. They lost a parent fairly young. They had fairly difficult health issues. They went through various friendship/ relationship/ financial problems. Throughout all of that though, they met a partner. They were extremely happy together. They had a close friend circle. They worked hard and, played hard.
Most importantly I suppose, they identified what brought them joy in life and they worked hard to get it. They were also supremely good at appreciating the good that they had. They were very good at appreciating things. Even simple things like their favourite film.
Kind of like they were able to wring out all the goodness they could find in life. I really admired that about them. I found it pretty difficult to emulate them though! Maybe some of my happiest moments were with them though so- perhaps it was contageous to some extent.
But yeah sure, I think some people can be reasonably happy in life. Not deriliously so all the time but, enough to make it seem like a positive thing to have experienced.