It has been said: Action expresses priorities. The key to a character's personality is his/her actions, especially under pressure. The focus on character actions also aligns with the showing rather than the telling of a narrative. Similar to my blog on "Dialogue in Fiction", 'unspoken' dialogue is pretty much just character actions that are integrated into a dialogue which may also include a character's internal thought.
What makes action possibly the strongest of character methods is its ability to appear just about anywhere. This includes how a character lights her cigarette, the way she organizes her bookshelf, the way she keeps every door in the house closed until she needs to use another room.
In The Three-Body Problem by Liu Cixin, Wang Miao meets Captain Shi Quiang for the first time. This interaction occurs after a forty-year time-skip from China's Cultural Revolution. With this context, the reader should expect a change in the atmosphere, which will be felt immediately at Wang Miao's confrontation with the armed police. The introduction of Shi Quiang, nicknamed Da Shi, first includes Wang Miao's physical description of him:
As soon as Wang saw the cops, he felt annoyed. The younger one was all right - at least he was polite. But the other one, in plainclothes, immediately grated on him. He was thickest and had a full face of bulging muscles. Wearing a dirty leather jacket, smelling of cigarettes, and speaking in a loud voice, he was exactly the sort of person Wang Miao despised. "Wang Miao?" (p.51)
With this impression in mind, the character and reader get to see Da Shi in action:
The way the cop addressed him by name only, so direct and impolite, made Wang uncomfortable. Adding to the insult, the man lit a cigarette as he addressed him, without even lifting his head to show his face. Before Wang could answer, the man nodded at the younger cop, who showed Wang his badge. (p.51)
It may feel strange to feel some relaxed casualness from Da Shi, of whom Wang paints as rude. Two traits meld together, the physical description and the blasé way Da Shi carries himself. Though Da Shi is quickly disliked by Wang Miao, his actions balance the reader's perspective of him. The author offers something new with Da Shi's actions, revealing that Da Shi is comfortably familiar with this line of work. This is clear due to his casual greeting and him not lifting his face to meet Wang's gaze. It is treated not as unwillingness but almost a subconscious habit of how Da Shi operates, there is no nervousness, no excess in mannerisms whether polite or rude.
What makes Da Shi such a fun character to explore might be because he is not the protagonist and many of his choices are not as markedly high-risk as that of Wang Miao's. Regardless, Da Shi is not excluded from performing under pressure. In a tense stand-off between an extremist group, the Earth-Trisolaris Organization (ETO), and the police with Wang Miao in between, an ETO member holds an explosive, threatening to set it off. The idea, shared by the police explosives expert, is to shoot the mechanism to set off a scattered and conventional explosion rather than a "precise compression", meaning the bomb's fully active potential. Da Shi must get a good shot of the bomb before the woman can set it off:
Da Shi stared at the nuclear woman, saying nothing.
"How about snipers?"
Almost imperceptibly, Da Shi shook his head. "There's no good position. She's sharp as a tack. As soon as she is targeted by a sniper scope, she'll know."
Da Shi stepped forward. He pushed the crowd apart and stood in the middle of the empty space.
"Stop," the young woman warned Da Shi, staring at him intently. Her right thumb was poised over the detonator. Her face was no longer smiling in the flashlight beams.
"Calm down," Da Shi said, standing about seven or eight meters from her. (p.280)
So far he is written with plain actions like "stared" and "stepped forward". There is a coolness drawn from this especially due to the nature of the moment. These movements also nod to self-sacrifice. He willingly steps out of the crowd to isolate himself from the others and target all attention to him. Now, Da Shi offers her an envelope with information about her mother. A bluff formulated by his skills in reading others:
Da Shi took two steps forward. He was now more than five meters from her. She raised the bomb and warned him with her eyes, but she was already distracted. One of the two ETO members who had tossed away fake bombs strode toward Da Shi to take the envelope from him. As the man blocked the woman's view of Da Shi, he drew his gun with lightning-fast motion. The woman only saw a flash by the ear of the man trying to take the letter from Da Shi before the bomb in her hands exploded. (p.281)
As slow and technical as this moment may seem, every sentence adds to the expertise behind Da Shi's movements. What may be overlooked is that he had to wait to draw his gun the moment the woman could not visually anticipate it. This means that not only did Da Shi need to remain calm and allow the ETO members to approach him, but he also had to refrain from reaching for his gun too early. The paragraph highlights Da Shi's skills in observation even under immense pressure.
It must be noted that Da Shi's actions in the introduction and his performance under pressure may be different. The examples provided are only fragments of Da Shi's development and role in the novel. All this to say that a writer needs to test his characters under intense circumstances and to embrace the value of consistency especially for characters that are as experienced and steadfast as Da Shi.