Yep, it's true.
But it may be different for everyone.
Well I had braces for 2 years, had to wear a retainer 24/7 for one year, and now I just wear the retainer at night... You're supposed to wear the retainer at night for the rest of your life..lol No, but seriously. That's what my orthodontist explained to me. It sucks, but it keeps the teeth from moving back. And trust me, if you don't wear it for like a month, your teeth DO move slightly and the retainer won't fit as well.... I would know:P BUT you can choose to have a permanent built-in retainer inside your mouth that isn't noticeable at all. It just goes behind your teeth, not in front. I didn't want that though... lol
If you think about it, wearing a retainer while you sleep isn't at all that bad, you actually forget you're wearing it, and no one sees you! You don't have to wear it EVERY night, bc sometimes I forget or Im sleeping over a friends house, etc.... But it's highly recommended because teeth DO move... :P It sucks, but yeahhh.