Final answer:
In the Mark Twain excerpt, the themes of self-reliance and external pressures interact to convey the message that one should trust their own knowledge and training amidst doubt, with the story's conflict illuminating this central theme.
Step-by-step explanation:
To analyze the themes of the Mark Twain excerpt, we must consider how they interact and build upon one another. One prominent theme is the importance of self-reliance. In the passage, Twain begins confident in his abilities to run a crossing, but the presence of Mr. Bixby and others causes him to doubt himself. This introduces the second theme, which is the impact of external pressures on an individual's confidence. As Twain second-guesses himself due to the increasing number of observers, these themes interact to develop the overarching message that leaning on one's own knowledge and training is crucial in the face of doubt. The conflict serves both to enthrall the reader and to build the theme: you must trust your own skills amid external doubts.
The narrative's plot and conflict inform its theme. As the story progresses, the introduction of external characters who induce doubt in Twain's character exemplifies how external pressures can erode self-reliance. However, the resolution of the story can imply that despite these pressures, one should adhere to their training and knowledge. It illustrates how the central conflict catalyzes the protagonist's realization of this truth, effectively marrying the themes of self-reliance and the influence of external pressures.