No one wants to plan for a loss but it is always better to be prepared. US have recently seen a real estate meltdown that has caused the entire economies of the world to go into recession. So, it is very important to foresee such meltdowns and be prepared for losses. A second income source will ensure that you have enough rotational money to see you through losses.
Most of us think of investment income as just the cash flow we get from bank interest, bonds, share dividends and property rents, some of which comes via a super pension.  But a more complete view is to also consider how growing the value of your investments can add to your spending potential.  This total return approach generates income from both income and growth to optimise spending from your portfolio across all market cycles, aligning cheap and expensive investments to your goals.