With the 1st generation of idols, there was a saying that "members-1=0." It meant that if any of the members were to leave, the group would become meaningless.

However, many more idol groups formed, and there was a period of 'idol warring states era.' As such, the aforementioned saying became a thing of the past. There are many members that leave their groups due to personal family problems, academic problems, incidents, accidents, career worries, and group personalities.

In Super Junior Jo Kyuhyun joined the group and Hankyung left. In KARA Kim Sunghee left and Hara and Kang Jiyoung were recruited. Nicole left the group not too long ago to pursue her studies. Wonder Girls' HyunA and Sunmi left the group, and Kim Yoo Bin and Hyerim joined. Most recently An Sohee became an actress and left.

Jay Park left 2PM, leaving them with 6 members. TVXQ's Kim Junsu, Park Yoochun, and Kim Jaejoong left, leaving Yoonho and Changmin. The 3 members who withdrew from TVXQ went on to create a new group by the name of JYJ. U-KISS members Alexander, Kibum, and Dongho withdrew from the group.

After School was composed of members who graduated and were admitted to school, so there were quite a few members that were recruited and withdrawn from the group. Uee first joined, and Yoo Soyoung graduated. Afterward Raina, Nana, Lizzy, Leeyoung, and Kaeun joined. Bekah left the group. Recently oldest member Kahi graduated and went solo.

T-ARA first recruited Hwayoung, but she left shortly thereafter due to tension with the members. Areum joined but left after a short while. Nine Muses debuted with 9 original members, Rana, Jaekyung, Bini, Sera, Lee Sem, Euaerin, Eunji, Hyemi, and Minha. Jaekyung left the group and was replaced by Hyuna. Then Rana and Bini officially left the group, and Kyungri and Sungah joined. Most recently Lee Sem and Eunji left the group.

Jewelry debuted with Park Jungah, Lee Jihyun, Jung Yujin, and Jun Eunmi. When Yujin and Eunmi left, Seo Inyoung and Jo Minah were recruited. Thereafter Minah and Jihyun left the group, who then recruited Kim Eunjung and Baby-J (Ha Juyeon). And then Park Jungah and Seo Inyoung officially left. Park Semi and Kim Yewon joined the group. Recently Kim Eunjung left the group.

Hong Yookyung left A Pink. The group 100% became a five-member team when leader Minwoo joined the military and Sanghoon decided to leave. Mr.Mr's Hon joined the group late, but left after just 6 months.