The Martian Chronicles
How we cite our quotes:
[H]e saw the red fire and heard the big sound and felt the huge tremor as the silver rocket shot up and left him behind on an ordinary Monday morning on the ordinary planet Earth. ("The Taxpayer," 7)
The Taxpayer is surrounded by people (well, mostly cops right now), but he's still isolated, left behind by the rocket he thinks he should be on. This is a good example of Bradbury's point that isolation isn't always about literally being alone.
The captain had to join the dance. He didn't want to. His face was solemn. Spender watched, thinking: You poor man, what a night this is! ("—And the Moon Be Still as Bright," 53)
It looks like you can be emotionally isolated, too. All the other Earth Men are happy, while Wilder is always solemn. He won't throw his lot in with Spender or with Parkhill; and then, finally, he's sent off to explore the solar system. Talk about isolated.
"... you've a different way of seeing things, Spender." ("—And the Moon Be Still as Bright," 67)
Like the Taxpayer, Spender is lonely in the crowd. It turns out that he's right about humans destroying Mars—but he's also crazy. Maybe there's something to be said for agreeing with the majority.