Humans, humans! These risky things start in small supposedly "harmless" habits, like some wild chick I once knew. She would hang out like crazy, then drink and drive herself home in the wee hours. One time my friend and I passed by her place just to check on her. We found her in bed at 3PM, her apartment door unlocked. The first thing she asked us is if we had seen her car outside. Then she said she had no idea how she got home. "My car brought me home". We were horrified, but she was just laughing.