―Sadness to Joy in Long Term Memory
Sadness was first born when Riley was a baby; there, she met Joy, the first born emotion. When she caused baby Riley to cry, Joy pushed her aside and fixed the situation. Sadness was only used when Riley threw tantrums.
Sadness is literally the very definition and being of sorrow and gloom. She is hardly ever used because Joy is the boss and doesn't want Riley to ever be sad. Because of this, Joy treats Sadness badly. Secretly however, Sadness yearns to earn her place among the other emotions, even though the others do not believe Sadness has a purpose in the mind and almost always prevent her from trying. She is the most sensitive out of all the emotions, as she felt genuinely hurt by Joy's desertion because "Riley needs to be happy", which made poor Sadness feel she was truly pathetic.
Sadness is also smarter and has more common sense than the others, which proved expedient in the journey through Riley's mind, as she kept trying to warn Joy about the dangers of taking Bing Bong's "shortcut", which was really a dangerous place to go through, but nobody listened to her. She also suggested scaring Riley to wake her up, but Joy thought that giving her a fun dream would wake her up.
Despite her pessimistic disposition, she is very considerate and compassionate towards others; when Bing Bong was sad about losing his wagon, she sympathized with him and let him tell his true feelings, which made him feel much better. Unknowingly, this is because of Sadness' true purpose - her role is to tell others when Riley needs help. When Sadness is requested to take control after Riley's sorrow became evident, she is able to let Riley express her true feelings and helps Riley find happiness at last. After the other emotions finally accept Sadness, not only does Joy start treating her better but Sadness gains more confidence in herself as well, now that she has finally found her place.