Life Mastery Decoded

What is the good life? And what is life mastery?
Many play out a thought experiment, half for fun and half for real interest, to figure out or work out what can be used to identify what a good life is.
What does this thought experiment consist of? It consists in imagining in what words, when we already feel we have arrived at the end of life, we would summarize the life we have lived.

Through such an idea, if we really feel it and take it seriously, we may indeed be confronted with the challenge of finding out and knowing
(1) what is a good life or even the good life, and
(2) how to realize it.

By decoding life mastery, we find out,
(a) what life mastery consists of,
(b) what master acts of life and what life skills are required for it, and
(c) by what milestones and by what states of life it becomes apparent what degree and quality of life mastery is realized.