You sound like you have misinterpreted the advice and just didn't know when to quit and move on. Sounds like you continued to beat a dead horse, and expected it to wake up.
Pro athletes become pros by focusing on one sport, that's why there's very few dual sport pros (pro EU Football players, and NO pro baseball players) -- you can't become great at two things when you have split attentions.
Billionaires become billionaires by focusing on one big venture, they only have 20 ventures after they become billionaires. A great example is Matt Ishbia who just recently purchased the Phoenix Suns for over a billion dollars. How? He focused on his one business; mortgages. And now he can leverage himself in 20 different ventures, hire at will, and spread out into his wildest dreams. Every billionaire exemplifies this pattern ... one huge business >== huge wealth >== diversification into many businesses, many passion oriented.
Yes, and that's when you narrow your focus and pound the pavement -- and go from thousandaire, to millionaire, to billionaire.