A single income source is a single point of failure. If your only income is your salary and you lose your job, your income goes to zero instantly. Diversifying income reduces this vulnerability.

Income stream categories: Active earned (salary, freelancing — requires your time). Portfolio (dividends, interest, capital gains — requires your capital). Passive (rental income, digital products, licensing — requires upfront work then generates with less ongoing effort). The "passive income" category is overhyped — most "passive" income requires significant upfront work and ongoing maintenance. But portfolio income is genuinely passive once the capital is deployed.

The math of income replacement: to replace $60,000/year in employment income from investments, you need approximately $1.5M invested at a 4% withdrawal rate. This is the FIRE number. Every additional income stream reduces the capital requirement.

Practical income diversification for someone with a full-time job: (1) Maximize employer income first (promotions, raises, job changes for higher pay). (2) Build portfolio income (invest savings in dividend-paying index funds — even $10/month of dividends is a second income stream). (3) Develop one skill-based side income (consulting, freelancing, teaching in your area of expertise). (4) Over time, create one asset-based income (digital product, rental property, content). The goal isn't 10 income streams — it's 2-3 that meaningfully reduce your dependence on a single employer.