contentment and happiness, because no matter how many achievements, money, cars, and properties you have, without happiness and contentment, you can never satisfy yourself, you'll always be missing a piece.
Contentment leads to happiness yes but we can not tell our self how successful we are, it depends on the outsider to say. Although inside we can be fulfilled but success itself is not what we can say of ourselves but it is the public that will quantify our success based on different criteria and comparison with others, such criteria include your age, education, pair group, social glass, family history and inheritance because those also play some roles to how successful we can be.
If you consider the way to measure success is by how the public judges, of course you will never be satisfied with the success you get. I think it's only right that you don't feel satisfied and happy with what you have achieved if you have that mindset.
we as humans must always remember and be aware that basically humans have advantages and disadvantages, therefore interpreting humans have their respective limitations.
Assumptions or public judgments are very wild and their respective or varied points of view, you can't make everyone like you, there are certainly many who criticize or even insult. Maybe you will feel tired if you are looking for happiness and satisfaction depending on other people.
if success is the same as happiness, the ancient Greek philosophy (Stoicism) asserts that "happiness comes from what we can control" which means that it is contrary to your opinion, because we know that public opinion about us cannot be controlled. .
In my opinion, the definition of happiness and success is to have an affluent life and always can feel grateful for what you get.