Speaking of Cai Sainan, she is said to be one of the few friends of Chou Xinya, but this was only what Chou Xinya thought of herself. Cai Sainan never considered Chou Xinya a true friend, she treated her like a dispensable companion.
Chou Xinya was quite attractive, however, because she was an orphan and grew up in an orphanage, she hardly had any money. The money she earned from part-time jobs was all spent on tuition and meals. She simply couldn't afford to buy lots of pretty clothes to dress herself up like other girls.
Therefore, Chou Xinya, always clad in old clothes, was ostracized by the other girls in class. It was during this time of being shunned that Cai Sainan appeared and told Chou Xinya that she wanted to be friends with her.
It was precisely because of what Cai Sainan said back then that Chou Xinya, over the years, chose to forgive her no matter what she did to her. And it was this attitude that led Cai Sainan to become increasingly presumptuous.