What was Rule 91 in ‘NCIS’?

Mark Harmon’s Agent Jethro Gibbs spent decades dropping serialized homespun wisdom on his fellow NCIS characters in the form of numbered rules.

There were dozens of the things – 91, in theory, not counting repeats or enormous, unexplained gaps in the list. There was Rule 9, “Never go anywhere without a knife,” which TSA agents aren’t crazy about. There was Rule 20, “Always look under,” which is a great way to get Pennywise’d. “First thing’s first, hide the women and children” came in at number 44, which was a little counterintuitive, but who are we to argue with the stepdad from Freaky Friday?

That 91st rule involved an extra layer of enigma, thanks to the way that Gibbs’ affinity for it apparently burned so brightly that he named his boat after it – one of his boats, anyway. He had another boat, named after his wife Diane, but he burned that one in a sort of masculine Viking funeral for his failed marriage. Gibbs had a habit of doing stuff like that to boats.

At the tail end of season 18, the grizzled, suspended investigator took to the seas at the wheel of Rule 91, motored off toward that horizon, and exploded. Kind of.

Rule 91 on NCIS, explained

So what was Rule 91? According to – twist! – a shockingly un-exploded Jethro Gibbs at the start of season 19, it’s as simple as it is stoic: “When you decide to walk away, never look back.” It’s frustratingly similar to Rule 11, “When the job is done, walk away,” but you can’t blame Gibbs for letting that slip his mind: Once the job of writing Rule 11 was done, presumably, he walked away. Per Rule 91, he never looked back. He did, presumably, look under. Gibbs had a lot of rules about looking at stuff.

Not everyone on the NCIS team had the same love of Rule 91 that Gibbs did, with McGee expressing his distaste for this last rule to live by. He saw Rule 91 as a direct violation of Rule 1, “Never screw over your partner.” Adding to that frustration for fans of the series: The fact that there were actually two instances of “Rule 1,” with the second being “Never let suspects sit together.” Anyone that still had “Never let suspects sit together” fresh in their mind was probably pretty confused as to why McGee felt so passionately about it. They would, no doubt, take solace in Rule 51, “Sometimes you’re wrong.”