The Pollyanna principle (also called Pollyannaism or positivity bias) is the tendency for people to remember pleasant items more accurately than unpleasant ones. Research indicates that at the subconscious level, the mind has a tendency to focus on the optimistic; while at the conscious level, it has a tendency to focus on the negative. This subconscious bias towards the positive is often described as the Pollyanna principle.
The name derives from the 1913 novel Pollyanna by Eleanor H. Porter describing a girl who plays the "glad game"--trying to find something to be glad about in every situation. The novel has been adapted to film several times, most famously in 1920 and 1960. An early use of the name "Pollyanna" in psychological literature was in 1969 by Boucher and Osgood who described a Pollyanna hypothesis as a universal human tendency to use evaluatively positive words more frequently and diversely than evaluatively negative words in communicating.
The Pollyanna principle was described by Matlin and Stang in 1978 using the archetype of Pollyanna more specifically as a psychological principle which portrays the positive bias people have when thinking of the past. According to the Pollyanna Principle, the brain processes information that is pleasing and agreeable in a more precise and exact manner as compared to unpleasant information. We actually tend to remember past experiences as more rosy than they actually occurred.
Researchers Margaret Matlin and David Stang provided substantial evidence of the Pollyanna Principle. They found that people expose themselves to positive stimuli and avoid negative stimuli, they take longer to recognize what is unpleasant or threatening than what is pleasant and safe, and they report that they encounter positive stimuli more frequently than they actually do. Matlin and Stang also determined that selective recall was a more likely occurrence when recall was delayed: the longer the delay, the more selective recall that occurred.
The Pollyanna principle has been observed on online social networks as well. For example, Twitter users preferentially share more, and are emotionally affected more frequently by, positive information.