There are three jobs that can be pursued in Star Project: Singer, Model and Actor. The ending you obtain upon reaching Star level 50 (a sum of all individual job levels) is determined by which job level is the highest.
As each lesson will deduct another skill point at higher levels, certain jobs are more difficult to pursue with high skill points at higher levels. At current, the Actor job is the easiest to pursue with either the skill combination of vocal, memory and acting, or of wit, dance and speech. As the for the Singer job is the most limited in appearances, to the conflicting skill pair of vocal & dance, the Singer job is the most difficult to master.
Thus, especially for more difficult jobs like the Singer, a fine balance need be strike on whether to train skills higher for high level appearances or to pursue low-to-mid level appearances which are less energy-XP efficient.