In addition to just being a fantastic movie, A Quiet Place was the first time that husband and wife John Krasinski and Emily Blunt got to appear on screen together, but it almost didn't happen. While Krasinski both wrote and directed A Quiet Place, and thus had a significant amount of decision making power, he initially didn't ask his wife to join him on the recent film. While he says he and Blunt had always talked about working together, it seems that the idea of asking her to work on a film he was directing had some significant pitfalls regardless of what happened. According to Krasinski...
We'd always talked about working together, but we didn't want the story of us being married to supersede whatever story we could tell. I didn't want to pressure her, if I asked her and she said no, I wasn't sure how that would go for my day and if I asked her and she said yes to help me out or do me a favor that wouldn't go well either. I just didn't say anything.
It would be one thing if John Krasinski and Emily Blunt were both simply acting together on some other project but with Krasinski directing A Quiet Place, the relationship dynamic changes. If she had decided not to do it, which wouldn't have been surprising, then you just got rejected by your wife, which is no fun. If she said yes because she felt some sort of obligation even though she didn't really want to it, you have a whole other set of relationship problems. The way John Krasinski explains it in one of the featurettes attached to the new A Quiet Place Blu-ray, it was just easier not to ask.
As it turns out, however, John Krasinski didn't really need to ask Emily Blunt if she wanted to be in the movie, as that happened organically anyway. It seems Blunt was more than happy to have somebody else play the role, as she had been suggesting different actresses based on what information she had picked up discussing the film with her husband. However, that all changed once she actually read the script.
As I was pitching her ideas that I was writing in the script she started listing actresses that she thought would be good for the part and then one day we were on a plane together and she said 'do you mind if I read the script?' I'll never forget, she turned to me and she looked sick. 'You can't let anyone else do this movie.'
It seems that Emily Blunt didn't really see what her husband was working on until she read it, and once she did, she insisted on being part of it. Considering how important the character relationships are to the film, the real chemistry between these two only helped the final product. A Quiet Place is available on Digital and Blu-ray now.