One of the most loved shows on US television, How I Met Your Mother (HIMYM) had nine seasons from 2005 through 2014. But now, two years after it has gone off the air, show helmers Carter Bays and Craig Thomas have revealed the sitcom’s unusual inspiration: September 11th.

The two New Yorkers, who had been working as staff writers on the Late Show With David Letterman aspired to do something bigger. To which Bay said “It really was a ‘do it now or never do it’ moment. Life is short — this is something we want to do eventually, we should do it,”

“It was around the time of 9/11 and it was actually — and I feel like I’ve talked to other friends of mine that have had similar experiences — it really was a ‘do it now or never do it’ kind of moment,” Bays shared this piece of information with the audience at the opening of the 12th Annual New York Television Festival on Monday afternoon. “It was like, Life is short, this is going to be something we want to do eventually and we should do it. I think that had something to do with it.”

The creators of HIMYM starring Neil Patrick Harris, Jason Segel, Cobie Smulders, Josh Radnor and Alyson Hannigan, said the tragedy informed the tone of the pilot episode. “We have to write something bigger and with emotion, and [that] talks about twists and turns in life,” said Thomas. Bays added, “It informed HIMYM in very subtle ways. For two 29-year-olds to be writing something so nostalgic … [Because we learned:] Wow, life really is about chapters closing and things coming to an end, and things pivoting on an axis that will never pivot back.”

After wrapping the series in 2014, Bays and Thomas relocated back to NYC and are now developing new projects with Sony.