Meaning of the title, why is it called "Die Hard"?

I always thought it stemmed from the saying "old habits die hard"

Nobody had a chance.

I think it was just a catchy, cool-sounding title for an action film, meant to suggest the toughness of the hero. At least it makes more sense that "Nothing Lasts Forever," which was the title of the book it was based on, and which has no relevance to the story at all.

Most people don't realize that this was sort of a sequel to a 1968 Frank Sinatra movie called "The Detective." And as a result, Sinatra was offered the part -- but only because he was contractually entitled to first refusal of any sequels adapted involving the character. Sinatra had retired from acting by then, and everyone knew he'd turn it down. "Nothing Lasts Forever" was Roderick Thorpe's 1979 novel sequel to the 1966 novel "The Detective."

They made a lot of changes for the movie. The book protagonist, Joe Leland, is a fifty-something retired NYPD detective who has become an anti-terrorism expert. In the movie, they changed the name to the more macho-sounding John McClane, and made him younger and with no specialized anti-terrorism training -- probably to make him more of an everyman character. Also, in the book Leland is visiting his daughter, not his wife (and unlike McClane's wife, Leland's daughter goes out the window with Gruber and plummets to her death). Also in the book, the terrorists really are terrorists, with a political agenda, not just thieves using terrorism as a cover. I actually think that was a stroke of genius on the part of the movie scriptwriters, it makes a great twist, and make the villains look cleverer and more manipulative, and therefore arguably more dangerous.

They made a deal with the battery company. They had trouble financing the film so the battery company threw in a few million, but insisted they had to call the film "Die Hard." They wanted Bruce to be dressed as a rabbit in the beginning of the film too, but that was cut in editing.

https://images.search.yahoo.com/search/images?p=bruce+willis+as+a+rabbit&fr=yset_chr_syc_hp&type=hp-banner-v2Aug27&imgurl=https%3A%2F%2Fi.pinimg.com%2F736x%2Fea%2F53%2F11%2Fea5311e45d7951e9fa52beb270cfebc6--bunny-suit-bruce-willis.jpg#id=11&iurl=https%3A%2F%2Fd1w8c6s6gmwlek.cloudfront.net%2Fdesignteamshirts.com%2Foverlays%2F344%2F691%2F34469159.png&action=click

Because it do go down.