This is an opinion editorial by Mickey Koss, a West Point graduate with a degree in economics. He spent four years in the infantry before transferring to the finance corps.
I’m going to use the California Public Employees Retirement System (CalPERS) as a proxy for your general retirement system. According to investopedia, CalPERS invested about a third of its money in bonds with a target annual return for the fund of 7%. Bonds are referred to as fixed income because of their predictable coupon payments. They are used for income, not capital gains.