But why was Black Widow so willing to sacrifice herself? Where did she get the courage to do so? How did she arrive at that mindset? It looks like all of this will be explored in the Black Widow solo movie. In a media scrum after the Hall H panel at San Diego Comic-Con 2019, David Harbour who’s starring alongside Johansson in the film had this to say (via ComicBook.com):

I think that’s the interesting part of her narrative is that we get to go back and explore this period of time between the events of Civil War and that particular arc. One of our things is we’ve known each other for a really long time and that relationship plays into the stuff that’s come beyond. The great thing about knowing the end of an arc, you get to go back and either foreshadow or play against it and it’s very joyful for fans to see these moments or prepped character beats come in at times.” Black Widow stars Scarlett Johansson, David Harbour, Florence Pugh, Rechel Weisz and O-T Fagbenle. It’s being helmed by Cate Shortland (Berlin Syndrome) from a screenplay by Jac Schaeffer and Ned Benson. Black Widow will be released in cinemas 1 May 2020. 

Black Widow Movie Will Explore Character s Tragic Choice in Endgame - 69