Road trip tent camping anyone?

The first time I went to Yellowstone I went there totally unprepared (1974). We got there at 2 AM and had no idea where to go or where to sleep. We were super tired from driving all the way from S. Texas. So we just found a spot between some tall trees and slept on the ground (no tent). It was a little cold but not too bad. The next day we ran into a park ranger and told him where we slept..................He said that we were lucky that we weren't eaten by a bear!!!! Young, dumb and stupid will save you every time???