The author's interest in investment philosophies stemmed from an NYU Stern MBA seminar where diverse investor viewpoints caused student confusion. He observed that few active investors consistently outperform the market due to its difficulty and the impact of luck. He notes that successful investors use drastically different approaches, challenging the notion of a single "best" philosophy. The author's conclusion is that each investor needs a tailored philosophy reflecting their beliefs and personality. He defines an investment philosophy as distinct from strategy or slogans, emphasizing its importance in avoiding negative consequences like chasing past winners or falling for scams. The book and online class aim to help investors develop their own tailored philosophies. The author outlines the choice between active investing versus passive indexing and investing versus trading. Within these groups, there are opportunities for further specialization, based on belief in how to exploit market mistakes. The author's latest book and updated online class provide further resources for investors.