NCIS’s Mark Harmon Reveals His Favorite Gibbs Rule & It’s Surprisingly Practical

Mark Harmon first appeared as Leroy Jethro Gibbs in a two-part episode of JAG called “Ice Queen” and “Meltdown.” He then played Gibbs on NCIS for the show’s first 18 seasons, plus the first four episodes of Season 19—nearly 20 years in total. Throughout that time, fans of the CBS drama learned about the many personal rules Gibbs lived by. Harmon says the rule he finds most valuable is also the most useful in everyday life.








