There is a reason my SS check is just about enough to feed our cat: absolutely tiny SS taxed income for just barely the required number of quarters. My total SS taxable lifetime income is about 1/3 of our current annual AGI. Our NW is more than double what the Millioraire Next Door's formula suggests as adequate.
Easy: Buy horribly run down property, do your own work, rent the property out (making "unearned income"), roll every dime you can shave off back into more property, pay off loans ASAP, persist for decades...