<p>The roommate ASKED her as a favor to leave the door open, and the OP agreed. That was a mistake, but the roommate still influenced the door being unlocked by ASKING FOR THE FAVOR. How can you not see that??? This is so typical, people don’t consider any social factors/influences on others behavior, think that everyone makes rational choices and have absolute free will, but they DON’T. The bottom line is, if it hadn’t been for the roommate asking to leave the door unlocked, OP would have locked it and no theft would have happened. I don’t know how much clearer this can get.</p>