To what extent is the protagonist of the story "Paul's Case" responsible for the conflict he faces?

I would argue that Paul is largely responsible for his predicament. Let us look at the evidence. Paul lives in a fantasy world in which he imagines himself to be a member of Pittsburgh's wealthy social elite. But instead of doing something—such as working hard or studying—to become just like the people he admires, Paul simply indulges in idle fantasies. This leads him to take a shortcut to living out his dreams by stealing from his employer and heading off to New York. Even with all this money burning a hole in his pocket, Paul does not put it to good use. He simply wastes it all on living out the fantasy of a wealthy young man about town.
In choosing to live in this fantasy world of his, Paul makes it virtually impossible for himself to live in the real world. It is no surprise, then, that he should take his own life. If he cannot live in the real world, then he must die in it. Though undoubtedly tragic, there is no doubt that Paul's demise is the inevitable outcome of the many bad choices he has made throughout his short life.