Diversification
Definition
Spreading your money across different types of investments so one bad investment doesn't tank your whole portfolio. Own stocks, bonds, and maybe real estate. Within stocks, own different industries and geographies. The goal is to reduce risk without giving up too much return.
Why It Matters
Diversification is risk management. A diversified portfolio of 100 mediocre investments usually outperforms betting everything on one brilliant investment (which rarely works). It lets you sleep at night during market volatility.
Example
Portfolio A: $100,000 all in Tesla. Tesla drops 50% in a year, you lose $50,000. Portfolio B: $80,000 in index funds, $15,000 in bonds, $5,000 in real estate. Index fund drops 20%, bonds up 4%, you're down ~$13,000 or 13% instead of 50%.