When I’m unhappy, I feel like I’m doing life wrong. I’d rather be happy. But is happiness the point of life, or is there more to it? If I pursue happiness, mine first then for those around me, is that selfish? But if there’s a bigger purpose, then what about people with Alzheimer’s or dementia who can’t recall recent experiences or make plans?
It probably matters to people who are looking for an external source of meaning, and doesn’t matter to people who are creating an internal source of meaning. In that way, it’s maybe a useful clue to what type of meaning is more valid.
In the scenario you gave, how would you judge whether a life was well lived? How would you go about living a good life? What would you do or become to be an effective human being?
You mean in the no-free-will purposeless-universe scenario? I think there's no right or wrong answer, really. Every human being (and animal, and plant, and rock) are simply what they are. You have to add somewhat arbitrary personal criteria to get a meaningful answer.
Personally, I think being kind and strong is very important. That's not very original, but I guess the interesting thing I have to say about it is that 99% of the population earnestly tries to do that, and the reason people suck is basically down to a version of Hanlon's razor. To be an effective human being, don't lie to yourself.
We all lie to ourselves. But I admire people who try to lie to themselves less, who try to be honest with themselves and face reality.