Think back to The 40 Year Old Virgin, during a throwaway joke, when Paul Rudd's character marvels at a DVD playing The Bourne Identity and says, "You know, I always thought Damon was a bit of a Streisand, but...I think he's rocking the shit in this." In one (likely improvised) line, Rudd somehow boiled down a once-wunderkind's entire career. Yeah, Matt Damon got his start doing a lot of crying and convincing us he was whichever troubled, bright young man he was playing. He was good at it. These days, Damon can alternate between likeable and smart everyman with great comedic timing and the brooding assassin that earned him Rudd's dubious praise.
The hit bestselling book The Martian, by Andy Weir, doesn't spend a whole lot of time developing Mark Watney as a character, and for obvious reason. Since Watney has literally no one to interact with save the reader, his character can largely be described as "resourceful," or "clever," or in his most three-dimensional "mirthful" or "kind of dorky." Mark is a scientist, and a damned impressive one, as his general knowledge helps him survive alone on the surface of Mars and even plan his own departure and rendezvous with a rescue ship. But nowhere in the book is Watney giving a soliloquy about his fear, or his hopes and dreams of making it back to Earth, or his loneliness or sorrow. He mostly moves on to the next problem that needs solving. Weir, an engineer who wrote the book in serial form online, likely lends himself to his protagonist in this way. So when it came time for Damon to pull on a pressure suit and shoot his own sci-fi version of Cast Away, with Ridley Scott's cold camera lens serving as the only stand-in for the friendly volleyball, things got rigorous.
Damon has an unqualified success of a performance, injecting the character from the book with a decisive authority required of astronauts, a boyish charm to convey the underdog perseverance, and a ragged shameless frustration and eroding sense of social awareness that express the true human reaction to the impossible situation.
The moment we're looking at comes more than halfway through the film, when Watney has finally gained access to radio transmissions from his crew after months of first being totally cut off from the human race, and then only conversing in complicated code systems and text. A particularly determined man who defied all odds and survived alone on a desert planet hears the first voice message he's received after endless weeks of solitude--the voice of Jessica Chastain as his confident mission commander--and he breaks down. For even the briefest of moments, the unstoppable force of Mark Watney's intellectual pursuit of survival cracks, and we see across Damon's face at least seven different emotions flashing in micro-expressions lasting less than a second each. He is delighted to hear someone talk to him. He is desperate to cling to this human connection. He realizes soberly how long it has been. He recognizes how tired and worn out he has become. He is uncertain if he will ever get to speak face to face with another person again. He despairs that this might be the closest he ever gets to another person for the rest of his life. He is determined to push that dark notion away and get to work.
According to Damon himself, this moment was the result of Ridley Scott unexpectedly piping in the audio of Chastain and the rest of the astronaut actors into the leading man's helmet. This was late in the film's production, after all the other actors had wrapped and Damon had been alone shooting his character's accidental exile...just him, Scott, and the camera for weeks. It's an amazing bit of directing, to be sure, but it's also a brilliant actor who recognizes in that split second how his character's situation relates to his own, and extrapolates the truth of that specific (fictional) person's reaction. Sure, Watney cracks wise throughout the film and makes sarcastic, deadpan comments to the camera about how total screwed he is, but in this moment the character becomes a person. Fragile. Chaotic. And true to the type of man he is, he recovers quickly and resolves to move forward.
Damon might have been "a bit of a Streisand" when he was crying in Robin Williams' arms or staring hauntingly past Denzel Washington in the late 1990s. But almost 20 years later into his career, he showed the vulnerability and empathy between himself and the fictional man he brought to life, if only for a moment. And he rocked the shit out of it.