Why do you get treated like crap during the first year of public safety jobs?

I'm about to graduate the Border Patrol academy in a few weeks. The consensus among my instructors is that we are going to get treated like crap our first year. Talking to a few of my class mates who have prior law enforcement that seems to be the norm where ever you go. I was really hoping once I got done with the academy I wouldn't have to be treated like a POS anymore. What is the purpose of treating new employees like this?