Group 1 - The core idea of the article emphasizes the importance of understanding index funds and their investment strategies to achieve good returns [2] - The article introduces a free course that provides insights into index fund investment techniques, including course notes and mind maps for efficient learning [2] Group 2 - The first principle of index funds is discussed, highlighting that low cost is more critical than market efficiency [9] - The historical context of index funds is provided, noting that over a decade ago, the scale of index funds was relatively small, with active investors numbering in the millions and total assets only in the thousands of billions [8] - The article references John Bogle, the father of index funds, explaining that all stocks together equal the market index, and that the combined returns of all shareholders equal the market index returns, minus various fees [9]