The theme of "Mr. Know-All" by W. Somerset Maugham is the danger of judging others based on appearances and preconceived notions.
The story centers around a passenger on a trans-Pacific ocean liner, Mr. Kelada, who is disliked by his fellow passengers because of his brash and arrogant demeanor. They believe him to be rude and conceited, and they avoid him at all costs. However, as the story progresses, it is revealed that Mr. Kelada is actually a kind and generous man who goes out of his way to help those in need.
The other passengers, including the narrator, are guilty of making assumptions about Mr. Kelada based on his appearance and behavior, rather than getting to know him as a person. They allow their prejudices to cloud their judgment and they miss out on the opportunity to form a meaningful relationship with someone who turns out to be a good friend.
This theme is exemplified by the narrator's own experience with Mr. Kelada. At first, he despises Mr. Kelada and avoids him at all costs. However, after Mr. Kelada saves his life during a typhoon and helps him through a difficult time, the narrator realizes that he has been wrong about Mr. Kelada all along. He learns that appearances can be deceiving and that it is important to not jump to conclusions about others based on superficial things.
In conclusion, the theme of "Mr. Know-All" is the danger of judging others based on appearances and preconceived notions. The story serves as a cautionary tale about the importance of getting to know others before making assumptions about them. It teaches us to look beyond appearances and to see people for who they really are, rather than judging them based on stereotypes or prejudices.