Ken Banta, founder of the Vanguard Network, and Orlan Boston, partner at Ernst & Young, argue that every aspiring leader needs to have a side gig -- not to pursue a crazy dream or earn some extra cash but to enhance their skills, knowledge, and network in a way that benefits their existing careers. The key is to find meaningful and strategic roles that help you bring new insights and experience to your day job, and you can even let your boss in on your plans. Banta and Boston are the authors of the HBR article "The Strategic Side Gig."