A 2013 study discovered that this sort of suppressed fixation can cross over into your dreams. When study participants were asked to suppress thoughts about certain objects before sleeping, they reported higher frequency of said objects appearing in their dreams. Your subconscious clearly has no respect for your willpower. So come bedtime, try really hard to not think about that rooftop pool party with Beyoncé, and you might be really "disappointed" when you wake up in the morning (especially if you sleep on your stomach).