I know because many of the kids I grew up with (including one very close family member of mine) were convicted of felonies and sentenced to anywhere from 1.5 to 12 years in a federal penitentiary. Of the 9-or-10-some-odd kids I know who did time, less than half of them have gone on to lead normal, productive lives. Many of them are back in prison now. Bureau of Justice Statistics back up my experience. If you are a male between the ages of 14 and 17 who is convicted of a violent felony, your chances of getting re-arrested are better than 80% [1].
So, why is this? Well, in my opinion, based on countless conversations I've had with these individuals and others, it's practically unfathomable that any of them actually succeed in going "straight".
It's not rocket science. Imagine you're 17 years old. You've been hanging out with the wrong crowd, doing drugs, getting into trouble, and leading a scumbag lifestyle since you were 15 or 16. You get charged with a violent felony, tried as an adult, convicted, and sentenced to 5 years in a maximum security prison (where you get to meet and hang out with a plethora of other gang bangers, drug dealers, rapists, and murderers).
Now picture this. You make parole after 3 years. You're 20. You've got no high school diploma, no college credits, no work experience, no car, no money, and the only friends you had who aren't currently either 1) in jail or 2) about to be in jail are juniors and seniors in college and probably studying abroad in Asia or something while you're living at home trying to figure out what to do with your life. 3 of the most formative years of your young adult life have essentially been obliterated.
What are you going to do? After striking out at 5 or 6 other local establishments, McDonald's just became the latest to turn down your application (you have to tell them if you've been convicted of a felony and if you don't they'll find out when they do the background check). You might have earned your GED while you were in prison but the prospect of getting that pre-law degree you sorta once dreamed is looking pretty slim. What would be the point, anyway? You're not allowed to pass the bar exam. Maybe you should join the military. Oh, wait... they don't want scumbags like you carrying around an assault rifle.
Remember your codefendants? One of them lives right downstairs. He wants to know if you feel like "chilling" later. He just got an ounce of cocaine from one of his buddies and there's still a ton of beer left over from that party he had last night. Fuck it, you're not getting anything done in the next 24 hours, anyway. You're bored. You might be embarrassed to admit it, but you're lonely. Might as well crack open a cold one and try to forget your problems for a spell...
See, when you get convicted and sentenced, you may only serve 15 months in prison but you will be a felon for the rest of your life. And if you got arrested in high school then you don't have any "former life" to go back to. You are not educated. You have no friends. You are not hire-able. You do not have the right to vote. You cannot serve in our military. They're practically begging you to fuck up again.
And, unfortunately, most of them do.