failure is baked into the voluntary, self-directed, commercially run retirement plans system
First, figure out when you and your spouse will be laid off or be too sick to work. Second, figure out when you will die. Third, understand that you need to save 7 percent of every dollar you earn. (Didn't start doing that when you were 25 and you are 55 now? Just save 30 percent of every dollar.) Fourth, earn at least 3 percent above inflation on your investments, every year. (Easy. Just find the best funds for the lowest price and have them optimally allocated.) Fifth, do not withdraw any funds when you lose your job, have a health problem, get divorced, buy a house or send a kid to college. Sixth, time your retirement account withdrawals so the last cent is spent the day you die.
Not yet convinced that failure is baked into the voluntary, self-directed, commercially run retirement plans system? Consider what would have to happen for it to work for you.