Answer:
Dexter viewed his friends as having come from rich families while he viewed himself as having come from a middle-class family only.
His motivation for being "careful" is not to let his friends or anyone know that he actually didn't come from a rich family. He even lied about where he actually came from in order not to give them a hint.
Explanation:
Dexter Green's dream to become successful was meant to win the heart of Judy Jones whom he admired for long time. This is one of the reasons why he opted to go to an expensive college, the East Coast College.
After college, he invested in business and became a rich businessman. However, he separated with his wife, Irene (who's said to have a lesser beauty than Judy), and joined the army during the World War I.
Upon hearing that Judy was already married and lost her beauty, Dexter didn't feel anything for her anymore. This shows how he left his winter dreams.
