"How much you can safely take out of your retirement portfolio per year without running out of money over your retirement time horizon isn't just debatable: It's unknowable.... [L]ong-term-care expenses are a big wild card for many retirees' spending plans.... While there's no consensus on whether annuities are a must-have in retirement or which types of annuities to buy, there's little doubt that the lifetime income they offer is in short supply."