Why was Joan on the underground train?

M: Wow, your coat’s got very dirty. Did you fall?
W: Yes, I had a terrible experience on the underground train when I was on the way to work. I tell you, a man came up to me and pulled out a knife. He pointed it right at me.
M: Oh, no. Are you all right? Did he hurt you?
W: No, he didn’t, but he took my handbag.
M: Then what happened? What did you do?
W: I caught hold of his knife and he pushed me to the floor.
M: Oh, no. Why did you catch hold of his knife? That’s dangerous.
W: I don’t know. I didn’t think.
M: What did the other passengers do? Did they help you?
W: Yes. Two men ran after the robber and held him.
M: Did the police come?
W: Yes, the police were called and two policemen came and took the robbers to the police station.
M: What a story! Thank God, you are all right.