Is it established that personal success or happiness is primarily determined by personality and is largely independent of social identities? In a discussion about choices about occupation, I shared the image of this tweet. The following was one of the replies:


  Of course you can sit and complain about it, but it tells you about your own shortcomings be it laziness, cowardice, fears of all kinds lack of initiative etc.


Further the commenter pointed out that 


  Personal success or happiness after (everything else being equal) is determined by your personality.


He claims this using the theory of delayed gratification. His point being [from the wiki link]:


  In follow-up studies, the researchers found that children who were
  able to wait longer for the preferred rewards tended to have better
  life outcomes, as measured by SAT scores, educational
  attainment, body mass index (BMI), and other life measures.


Actually he might be right. I have no idea of modern cognitive science results. So I want to know the following:

Are there results in cognitive sciences that show personal success or happiness is determined by one's personality? And that any occupation failure is determined mostly by personal shortcomings and is largely independent of social identities?
This seems to me the old nature versus nurture debate and there is no real answer to this. However, I highly doubt that it is personality (as an inherent trait of you - nature) that's the most important factor for personal success. The question is what shapes your personality.

Family matters a lot, so building your personality over the right type of Childhood experiences seems to have strong effects on personal performance.

Yet, even such mundane things like names can have a huge impact on personal success regarding job oppurtunities.