Basic Trope: A character maintains a calm facade and/or continues to be able to think and reason while under pressure.
Straight: Smith develops a strategy in the midst of fighting Drake despite being scared.
Exaggerated: Smith calmly performs complicated mathematical calculations in his head in order to disarm a nuclear bomb that's at ten seconds on the clock while under heavy machine gun fire, with sirens and strobe lights going off around him.
Downplayed: Smith is too stupid and/or absentminded to recognize threats against him, and thus does not fear anything.
Smith is actually a cyborg, or has endured enough stressful incidents in the past to have deadened nerves.
A very important part of Smith's training was devoted to develop a fortitude that would allow him to keep his calm even under the most stressful situations; an important skill that professionals in real life, like combat pilots, have to attain in order to excel at their jobs.
Inverted: Smith breaks down in tears after stubbing his toe.
Subverted: Smith is dealt a critical injury, and breaks down under threat of his imminent death...
Double Subverted: ...but gets back up, steels himself and carries out the plan.