Final answer:
The theme that best fits 'The Terrible Old Man' is 'Things aren't always what they seem.' The story emphasizes not judging people solely based on their appearance.
Step-by-step explanation:
The theme that best fits 'The Terrible Old Man' is Things aren't always what they seem. The story focuses on an old man who appears feeble and uninteresting, but as the plot unravels, it is revealed that he has a horrifying secret. This theme reminds us that we should not judge people based on their outward appearance and that there may be more to them than meets the eye.
Learn more about theme in literature