If you're coming from east of Michigan avenue it's pretty easy to make that mistake and wind up on lower Wacker. Chicago has always (at least since probably the 70s) been the kind of city in which if you make a wrong turn you can wind up in big trouble.
We ended up accidentally on the South East side of Chicago one time, by Ohio Avenue, at 2 am. I was a kid. We were all loaded up in the car, on a trip, too.
By the grace of God, nothing happened.