Households dependent on a single income are fragile. Job loss, illness, redundancy can produce immediate financial crisis. Two streams of income — employment + freelancing, two earning adults, salary + meaningful investment income — provide resilience against single-stream failure.
Possible second streams
Freelance or consulting work in your field (weekend or evening). Investment income at scale (requires significant capital). Rental income (requires property). Online business or content (newsletter, course, ecommerce — long build).
Where this matters most
Single adults supporting themselves. Single parents. Households with one earner during partner career break. Industries with redundancy risk.
Build a second stream when first is secure. Compound effect on financial resilience is substantial. £500/month side income over 10 years can build £100k+ buffer.