Diversification is one of the first building block portfolio management concepts I ever learned in my first job in the investment industry. Our firm would create a Harry Markowitz efficient frontier chart for every client portfolio. The idea was to show that risk comes not from individual holdings but how those holdings work together to reduce overall portfolio risk. The interesting thing to me about producing these chart...

source: https://awealthofcommonsense.com/2024/01/the-holy-grail-of-portfolio-management/