You don’t need an income to sustain your current way of life
For many people the current way life is not obvious. People can't often see what is really important to them. This could be family, helping people, making the world a better place.
I really like the other 3 points and are pause for reflection.
Nassim Taleb gives some great examples in one of his books about how how much is enough is all relative. And i am reminded of Hans Rosling's famous talk on poverty. So maybe in answer to your question is there is no absolute answer and it's all relative. For some people it's even just about keeping score.
I agree there is no definitive answer, which is why I found it interesting to pose the question to the community.
The important part, IMO, is not what targets we reach, but that we feel satisfied, fulfilled and happy when doing so.