Cognitive fluency is a fancy name given by psychologists to describe something simple: most people prefer things that are easy to think about than those that are hard.
That's pretty intuitive albeit overly simple - but does cognitive fluency really factor into our daily lives? Perhaps more than you're even aware of, according to this article by Drake Bennett of The Boston Globe:
Psychologists have determined, for example, that shares in companies with easy-to-pronounce names do indeed significantly outperform those with hard-to-pronounce names. [...]
One thing that fools us, for example, is font. When people read something in a difficult-to-read font, they unwittingly transfer that sense of difficulty onto the topic they’re reading about. Schwarz and his former student Hyunjin Song have found that when people read about an exercise regimen or a recipe in a less legible font, they tend to rate the exercise regimen more difficult and the recipe more complicated than if they read about them in a clearer font.