We expect the title character of a movie to be the protagonist, and to be played by a well-known actor. So it is a little strange that in My Darling Clementine, which is a movie about Wyatt Earp and the gunfight at the OK Corral, the Clementine to which the title refers is just a big nothing, played by an actress you have never heard of (Cathy Downs). She is not even the most interesting woman in the movie, for that is Chihuahua (Linda Darnell).
Apparently the point is that Clementine represents the future, which is to say, civilization. And civilization is bland and boring, as opposed to the Wild West, where we have such figures as Wyatt Earp (Henry Fonda), Doc Holliday (Victor Mature), and the Clanton gang (Walter Brennan et al.). So only after the excitement of the gunfight at the OK Corral, when just about everyone of interest is killed off except Wyatt Earp and his brother Morgan (Ward Bond), who then ride out of town, can Clementine finally become important.
I guess director John Ford did not want civilization to be associated with disease, so he has Holliday die during the gunfight, instead of dying years later, as was in fact the case. Or maybe we just like it better that way. Who wouldn’t rather die spitting blood from being shot in a gunfight than die spitting blood in a tuberculosis hospital?