Why positive fantasies make your dreams less likely to come true

FTA:

    But ultimately, Happes and Oettingen believe that positive fantasies are
    likely to scupper your [chances] of obtaining your goals. "Instead of promoting
    achievement, positive fantasies will sap job-seekers of the energy to pound
    the pavement, and drain the lovelorn of the energy to approach the one they
    like," they write. "Fantasies that are less positive - that question whether
    an ideal future can be achieved, and that depict obstacles, problems and
    setbacks - should be more beneficial for mustering the energy needed to obtain
    success."