See it from her perspective: Stratt was conscripted into Project Hail Mary just as much as Grace or any of the other scientists who work for her. She has complied without complaint, even though it means putting thousands of deaths on her conscience, even though she knows she’ll be villainized by history, even though she suspects she’ll be imprisoned for life if not executed after launch. She sacrifices herself because it is what must be done to have the best chance of saving humanity. And when she asks Grace to make a similar sacrifice, he refuses. He refuses even though, unlike her, he won’t have to sacrifice his conscience and, unlike her, he’ll be remembered as a hero.

Now obviously, Grace deserved to choose his own fate and what Stratt did was wrong. She knows that. But she also sees Grace as astoundingly selfish for choosing himself over the entirety of humanity (even if some of that choice was motivated by a lack of self confidence) and, on a personal level, for refusing to see things from her perspective and sacrifice himself to spare her one more death on her conscience. Grace is betrayed when the closest thing he has to a friend murders him. Stratt is betrayed when the closest thing she has to a friend forces her into the role of murderer.

And Grace! btw! ALSO knew that!!!! He knew deep down that there was no other chance of this mission succeeding, that there was no one else who could conceivably fill the role, and he chose not to go anyway. Imo this makes his refusal to go INSANELY more selfish and cowardly (I love him but it must be said).

AND ANOTHER THING ☝ Stratt knowing that Grace had the gene and not telling him. For ages. She knew, and she didn't tell him, and surely she was keeping that info in her back pocket for a reason. Bc I'm sure she could figure out that if she told him he was qualified to go, he would have run as soon as he realized what was happening. She knew that about him. And she kept that vital information from him so he didn't even have a chance to make a choice until it was too late. Even that early, she knew he would run.

"come again?"

"i learn more from thinking machine. human gender preference. attraction to same gender, means word 'gay.' all eridian same gender." rocky stands straight up. "rocky come out to grace now. all rocky plural gay, statement."

"...wow, that's... rock, i'm not sure it makes much sense to apply human ideas of sexual orientation to a monogendered species."

a long and judgmental pause. then:

GOD, she does not want to do this. She does not want to force him into that ship. But unlike Grace, she doesn’t have the luxury of collapsing, because somebody still has to act. Somebody still has to make the impossible decision and live with it. And Sandra Hüller plays this so brilliantly because she never makes Stratt’s suffering loud. She keeps it all so restrained and controlled, but you can still see every tiny crack in her composure. She has to hold herself together while her entire world is falling apart.

And the thing is, for YEARS Grace was probably the closest thing she had to a friend. Someone she trusted, relied on, someone who actually understood the unbearable weight she had to carry every single day while the entire planet waited for extinction or salvation. And instead of meeting her halfway and carrying that burden together with her, Grace leaves her alone with it. Grace gets to unload all of his fear, anger, and panic onto her, and she STILL has to be the one who is held responsible. THAT is what makes me lose my mind every time I watch this scene. Because yes, from Grace’s perspective, Stratt betrays him. But from Stratt’s perspective? Grace betrays her, the mission, years of work, and honestly humanity itself. And on top of all that, she is of course also heartbroken for her friend. She has to sacrifice someone she deeply cares about, become the villain in his story, and still keep going. As Sandra Hüller’s character says in Sibyl, “Sometimes having a breakdown is a luxury.” And damn well it is for Eva Stratt.