The subtle, yet disconcerting, realization that people no longer work for your benefit anymore. This usually comes after graduation, when one goes for employment in the real world. Its the realization that no longer are parents there to nurture you, the school there to educate you, and companies there to woo you for your business.

Suddenly, its your job to put everyone else first. Its your job to care for other people, for you to instruct others. Its you who is now metaphorically licking the shoes of the potential customer who may bring a few extra dollars for your employers. You're not working for yourself; You work for your company, whose sole purpose is to make money to please the executives, the customers, and the shareholders. And while they will never admit it, the simple and plain fact is that you don't matter.

You are an means to an end, and the company will exploit that until you are no longer profitable.