Billy and Akaisha Kaderli both retired in 1991 at the ripe age of 38.
The former stock broker has lived through a series of market booms and busts, but the 2008 crash led Billy Kaderli to rethink his investment strategy.
The retiree sold some shares of a mutual fund he was invested in, and his account was placed under a 30-day hold. Not having access to his money led Kaderli to research more flexible options.
Exchange-traded funds, or ETFs, can be traded much like stocks, and gave Kaderli more freedom to move the couple's money around. That trading does come with more risk but can be useful for an informed investor, Kaderli said.
The funds are also tax-efficient thanks to their unique structure.
Check out this video for a simple breakdown of how ETFs work and to learn the risks and advantages you can expect as an investor.
Disclosure: NBCUniversal and Comcast Ventures are investors in Acorns.