Research suggests that a conscious desire for external illness gain can have internal unconscious effects, in that subjective symptoms can be heightened by external reward. This mechanism can be explained on the basis of Freud's later work, in which he mentions two types of resistance, which resemble each other—the need to be punished and the need to be ill. The concept of the need to be ill can explain why in modern society, with its established systems of support, regulations, and procedures that are conducive to illness behavior, patients who consciously strive for external gain can experience strengthening feelings of being ill and even deterioration without being aware of this process.