People with BPD can experience the world around them as a series of extremes – black and white, good and bad. These evaluations can vary rapidly, such as cycling between viewing a friend as a savior one week and as a traitor the next. Appreciating shades of grey and subtle differences, especially in interpersonal situations, may be very difficult for people with BPD. Instead, they may view people, circumstances, or influences as all good (idealization) or all bad (devaluation).

According to the National Institute of Mental Health (NIMH), these changes may be the result of how the BPD brain processes information coming in from the world. They found that people with BPD are more likely to read a neutral face as angry and to have more powerful reactions to negative words than people without BPD.