Back to the Basics: How to Manage Your Portfolio Without Overthinking It

What It Covers

Andrew Sather and Steven Morris conclude their "Back to the Basics" series by covering core portfolio management principles: diversification, position sizing, dollar cost averaging, entry and exit rules, and the most common mistakes that cause investors to destroy their own returns over time.

Key Questions Answered

• •Diversification baseline: Build a portfolio of 15 to 20 stocks before considering selling any position. Academic research shows diversification benefits diminish beyond 25 stocks, while holding fewer than 10 creates unnecessary volatility. Buy one stock per month to reach this target, giving you roughly 18 months to develop stock-picking skills progressively.
• •Position sizing by strategy: High-conviction value investors should target 5 to 6% per position, mirroring Andrew's personal framework. Ultra-growth investors buying early-stage companies should hold 50 to 100 positions since few winners carry the portfolio. Warren Buffett allocated 25% of his portfolio to Coca-Cola only after years of research and extreme conviction.
• •Dollar cost averaging through downturns: Consistently investing monthly, regardless of market conditions, outperforms market timing because the largest single-day gains frequently occur during bear markets. By the time economists officially declare a recession — which requires six months of data — the best recovery days have already passed, making exit strategies counterproductive.
• •Sell triggers to follow: Sell when business fundamentals deteriorate, not when prices drop. Two reliable rules: exit immediately if a company cuts its dividend, and exit if debt levels rise to unsustainable ratios without productive deployment. Avoid selling winners to rebalance toward underperformers — Peter Lynch's framework describes this as cutting flowers to water weeds.
• •Portfolio guardrails against tinkering: Opening a brokerage account daily and making frequent trades is one of the primary ways investors damage long-term returns. A practical solution is maintaining a separate, small "play" account with a fixed monthly allocation for active trading, keeping speculative behavior isolated from the core long-term portfolio.