I put 80% of my money in the S&P after Howard Marks told me not to

What It Covers

Sam Parr and Shaan Puri examine a 2014 Swedish twin study finding that 45% of investing behavior is genetically determined, then connect this to self-knowledge frameworks for business and career decisions, before pivoting to YC's latest startup requests covering aesthetic data centers, AI company management structures, drone defense, and AI-personalized medicine.

Key Questions Answered

• •Genetic investing bias: A 2014 Swedish study of 30,000 twin pairs found 45% of investing behavior is genetically determined. The six measurable biases are: holding too few stocks, excessive trading, performance chasing, home country bias, preference for lottery stocks, and refusing to sell losers. Identifying which bias you skew toward most allows you to build specific guardrails before making financial decisions.
• •Change requires experience, not reading: The Swedish study found that education level and book consumption did not meaningfully improve investing behavior. The only factor that produced measurable change, beyond genetics, was working directly in finance — experiencing real losses firsthand. Reading about cognitive biases, as Daniel Kahneman himself admits, does not prevent you from suffering those same biases in practice.
• •Match your game to your personality type: Monish Pabrai discovered through a 360-degree personality assessment that he was suited for solo, competitive, numbers-based games — not team management. Switching from running a $6M revenue company to solo stock investing produced dramatically better results. The framework: identify whether you perform better in solo vs. team, competitive vs. collaborative, and numbers-based vs. relationship-based environments before choosing a business model.
• •Pre-commit decisions to override future bias: Four tactics counteract genetic investing tendencies: pre-commit decisions in writing before emotions activate (e.g., document firing criteria at hire); shorten feedback loops to get scoreboard data faster; stay within your zone of genius rather than playing games where your specific bias is fatal; and use activity substitutes like reading or hobbies to reduce destructive portfolio tinkering during periods of inaction.
• •AI as company brain, not assistant: Jack Dorsey's restructuring at Block reflects a model where AI functions as the central decision-making brain while humans serve as information nodes feeding it context. Citrini Research illustrates this shift — their analysts now do fieldwork gathering first-party data (one researcher physically entered the Strait of Hormuz by boat) rather than building spreadsheets, because AI outperforms humans at data synthesis but cannot gather ground-level reality.
• •Opportunity windows shift with each tech wave: Each major tech cycle produced winners who looked nothing like the previous cycle — social networks gave way to real-world marketplaces (Uber, Airbnb), then crypto, then nonprofit AI research labs. Current signals suggest the next wave centers on hardware, robotics, defense tech, and drone swarm defense. YC's request-for-startups list now includes low-cost drone countermeasures, as a single Iranian drone swarm destroyed an AWS data center that lacked defense systems.