2. Kirk orders the Enterprise into the Neutral Zone
In the TOS season 1 episode "Balance of Terror," Captain Kirk and the Romulan commander (Mark Lenard) have a tense submarine-style fight near the Romulan Neutral Zone. Starfleet has made it very clear that Kirk can't go into the Neutral Zone and that the Enterprise is expendable.
To stop this deadly menace, Kirk chooses to follow the Romulan ship into the Neutral Zone, breaking regulations and jeopardizing a fragile truce. His decision is shown as a thoughtful, difficult one taken by a captain who won't let political implications stop him from saving lives.
Kirk is intriguingly stubborn and empathetic. As shown in his final conversation with the Romulan commander, who admits they might have become friends in a different reality, Kirk's greatest strength is his ability to combine human and military understanding.