Still thinking about this major difference between the book and the movie. This is the paragraph right before Grace remembers he did not go onto the Hail Mary willingly. He's still holding onto preconceived notions of what he must have been like in the past to inform his current mindset. That's why the decision to go back and save Rocky has a lot more emotional attention in the book. He's still not sure if he's capable of brave decisions until he makes that one.
Whereas in the movie, we've already seen Grace's growth in courage. He went from backing out of his first EVA (and failing LOL) to voluntarily risking his life jumping off of the Hail Mary to retrieve the Adrian sample collector (to Rocky's disapproval). There wasn't a single moment of self-doubt there. He locked in in a way he'd never done before. He's proven to himself that he's capable of making brave decisions. It doesn't matter as much to movie Grace whether he'd made brave decisions in the past - he's making them now.
The big reveal in the movie comes later, as a contrast to Grace's celebratory mood. It's not so much a predictor of Grace's future actions as it is just a reflection of his self-image.
That's why the decision to save Rocky came with less angst in the movie, and even came with happy Beatles music. At that moment, he was already the person capable of saving a friend at the cost of his own life. What he did in the past no longer has any no bearing to how he sees himself now.