I saw a staggeringly wrong post (I think from the same source as this take) about how TOS Kirk doesn't experience any meaningful suffering or angst, he just gets frustrated by challenges to his authority/command. The idea of him having real angst is just made up and projected onto him by fandom. Yes, this is the same James T. Kirk who feels the need to log this thought process: "No man achieves Starfleet command without relying on intuition, but have I made a rational decision? Am I letting the horrors of the past distort my judgment of the present?"
It feels almost like cheating to bring up the most obvious counter-examples tbh, but I actually find it really interesting that Kirk's most haunting fears/vulnerabilities throughout a bunch of episodes are so persistent and clear throughout the show as a whole. A major one, for instance, is his loneliness/dread of being abandoned to solitude. Ignoring everything except TOS:
HELEN: The machine wasn't on high enough to kill.
KIRK: But he was alone. Can you imagine the mind emptied by that thing? Without even a tormentor for company.
SPOCK: He thought you'd like to know the treatment room has been dismantled and the equipment destroyed.
KIRK: Thank you.
MCCOY: It's hard to believe that a man could die of loneliness.
KIRK [staring into the distance while the camera focuses on his almost blank eyes]: Not when you've sat in that room.
"Conscience of the King":
LENORE: At the party, you were such a brash young man.
KIRK: And now?
LENORE: Now somehow different. Not a ship's captain with all those people to be strong and confident in front of. You know, you're really very dear, aren't you? In some ways, very lonely.
MCCOY: Mr. Spock, the man on top walks a lonely street. The chain of command is often a noose.
KIRK: Except for myself, all crew personnel have transported to the surface of the planet. Mutinied. Lieutenant Uhura has effectively sabotaged the communications station. I can only contact the surface of the planet. The ship can be maintained in orbit for several months, but even with automatic controls, I cannot pilot her alone. In effect, I am marooned here. I'm beginning to realize just how big this ship really is, how quiet.
"And the Children Shall Lead":
KIRK [provoked by the alien's powers into a panicked meltdown rooted in his deepest anxieties]: The ship is sailing on and on. I'm alone. Alone. Alone.
"Is There In Truth No Beauty?":
KOLLOS [through Spock]: But most of all, the aloneness. You are so alone. You live out your lives in this shell of flesh. Self-contained, separate. How lonely you are. How terribly lonely.
"Requiem for Methuselah":
SPOCK: The epidemic is reduced and no longer a threat. The Enterprise is on course five one three mark seven, as you ordered.
KIRK: A very old and lonely man. And a young and lonely man. We put on a pretty poor show, didn't we?
