It works both ways. I think I'm more likely to take advice from someone who appears successful in their field.
Perhaps the choice to work on something they're truly passionate about helped them to be successful, while others who merely did what was expected did not have the drive to excel at it.
"I think I'm more likely to take advice from someone who appears successful in their field."
Problem is he's not giving you advice tailored to your specific situation. He is giving general advice. And with any general advice it's hard to account for all the nuances and judgement that might change with knowledge of specifics.
General advice might be "marry someone with a good education" or "marry a doctor". But a Kennedy might have good education but they also come with a host of other issues (and benefits) as a result of their fame and family name. With respect to the latter I'm sure Zuckerberg marrying a Physician is less important then it would be to someone else who could benefit from the stability and income that occupation brings.
Perhaps the choice to work on something they're truly passionate about helped them to be successful, while others who merely did what was expected did not have the drive to excel at it.