CNN's John Sutter says he joined the U.S. Army a little over 20 years ago and decided to get out four years later. Sutter: Most of my adult life has been spent in the military, until a year ago. He says it's the two and a half weeks getting to that point that’s hard for some, but it's not the same across the board. "I thought this was the hardest thing I’d ever done in my 18 years of existence," he says.