Idealism/Pragmatism dichotomy:The belief that being practical and having moral principles are in opposition, and you must choose one or the other.
This belief is a derivative of the Moral/Practical dichotomy.
Idealism is the belief that we should adopt moral principles, even if they have negative effects on our lives. The idealist is willing to suffer in order to do what he thinks is right. An example of an Idealists is a monk who takes a vow of poverty, sacrificing his material interest in order to stick to his moral ideals.
Pragmatism is a rejection of Idealism. If the Idealists principles get in the way, the Pragmatist solves it by rejecting moral principles. They do whatever is deemed as practical, with no concerns for morality. Politicians are often examples of Pragmatism, doing whatever it takes to get reelected. The problem is that principles are generalized knowledge that allow you to predict the outcome of certain kinds of actions. By rejecting principles, you have no means of determining what might be practical.
These two positions form a false dichotomy. The Idealism rejects practicality for the sake of moral principles. The Pragmatist rejects moral principles for practicality. But that all hinges on the view that moral principles are in conflict with what's practical, instead of means to being practical. It assumes that they're mutually exclusive. But if you adopt a morality of rational self-interest, where your morality seeks to enhance your life, your moral principles become your means of determining what kind of actions will be practical.