They tell you straight off the bat that you're not going to come back from Parris Island the same as you were before. I didn't believe them until I made it off that island. Here's what changed.
1. Tolerance
It might be a little bit of a surprise, but Drill Instructors get very mad when you don't do what they ask with some sort of speed and intensity. They get mad when you give excuses or when you complain. That rubs off on new Marines. Your tolerance for slowness, stupidity, and just about everything stupid is so low that you don't know what to do with yourself. You're left knife handing every single person you see.
2. Anger
Along with a low tolerance for stupid people and slow people you'll find that you'll get pissed a lot easier. It's small things big things, things you never paid attention to before. And you try to have some sort of bearing but you'd be lying if you said you didn't want to go full on Drill Instructor and blast some people.
3. I Don't Care
The funny thing about boot camp is that it has this ability to make you appreciate what you had back home and the freedom you have. Where I might get bothered by certain things like drinking, smoking, excessive cursing before... yeah you do you boo. Live life because honestly, I don't care. If you dont like me, good on you, I don't care.
4. Responsibility
The thing is, you're expected to act a certain way, talk a certain way, walk a certain way. You have this responsibility to present yourself in a way that makes the Corps look good. You have a responsibility to your Marines to be on top of your game. To your country, that you'll be their first line of defense. It's a lot of weight to carry, but it's only another piece of the puzzle.
5. Physical Changed
You won't eat slow again for a hot minute. You will have this weird ability to sleep almost anywhere. And you'll have this uneasy need to PT when you miss a day. You've lived this lifestyle for a lil while...you get in this cycle. And we all know you don't really want to give it up.
Boot camp changes people. It's a rough environment with loud and insulting people that you eventually start to look up to. You may think they're Satan's spawn but to me, they're family. Marines are different kind of breed and you won't understand until you're around then all the time. But even then, I wouldn't trade this for anything.