What is the main factor that Robinson wants to show us in "Richard Cory"?the idea in the poem
The main idea in the poem is that appearance and human value do not always coincide. In the poem, Richard Cory is seen by other people as having it all. He has a great reputation. He looks good. People think highly of him.
However that is just surface reality. Underneath all of that is a sad and lonely man who kills himself.
The idea is: do not judge another person's life or happiness by what you see on the outside or by their external achievements.
The inner life of a person can never be known.
You might be able to boil the poem down into one statement: Don't envy the rich!
The previous poster's comments are right on the mark but don't address the lines
In fine, we thought that he was everything
To make us wish that we were in his place.
Exactly why Richard Cory kills himself isn't explained or even hinted at in the poem. Maybe he was indeed sad and lonely, or maybe he was being blackmailed. Who can know what was really going on inside the man, indeed.