In 2012, even I wrote a 150-page eBook about severance package negotiations that still regularly sells about ~35 copies a month at $85 each (2nd edition for 2017) without any effort. In order to generate $2,975 a month or $35,700 a year in passive income as I do now, I would need to invest $892,500 in something that generates a 4% yield! To earn $10,000 a year in passive income would therefore need roughly $250,000 in capital.
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.