During his time in Root, Sai was ordered to eliminate a large number of individuals that posed a threat against Konoha.
This causes him to break out of his emotionless shell and start to remember the times he had with his own "brother", Shin.
Realising he was offending people by saying characteristics that came to his head, Sai decided to take a different approach by saying the opposite of what came into his head.
In this way, at the same event Sai called Ino "gorgeous" (although he truly meant to call her "ugly"), much to Ino's surprise, Naruto's relief, and Sakura's outrage.
Though largely successful in this regard, Sai retained an interest in art.
When Shin, an older Root member, discovered Sai's drawing ability, he encouraged Sai's talent and they became very close.
In the anime, it was shown from his Infinite Tsukuyomi dream that his greatest desire is to fully rediscover his emotions and connect with as many people as possible through it.