Would somebody please tell me the theme of the Third Expedition in the Martian Chronicles? In other words, what is Mr. Bradbury trying to say about life in general?
So far I like the facts that the people were in hopelessness but blinded by their perception.

Look at the captain's speech. Basically, things are often not what they appear. It's a great commentary on the human nature of people seeing what they want to see unless they've lived long enough to be cautious and suspicious.

Like Heller's CATCH 22, this story also ponders the nature of sanity/insanity, and how the determination of a person's 'sanity' can be purely a matter of perspective. Note the Martian psychologist's seriously flawed logic!

Apologies! My previous post refers to 'The Earth Men', not 'The Third Expedition'.