One day, at the end of a training session, I was in a carpark by the Thames talking to a friend. It was late - 10 pm, and it was dark. We were outside our rowing club, but everyone else had gone home. The club is a little bit isolated for London, in a dead end street with a crematorium next door and few neighbours except for the recycling centre. A few hundred metre away you'd be protected by street lights and passing cars, but just in the carpark, anything could happen.
A woman ran towards us from the riverside tow path. "My boyfriend is chasing me. I think he wants to hurt me." I sized her up, and knew straightaway that if she pulled a knife on me, she'd win. There were two equal possibilities - that she was in trouble and I could easily help her, or she wanted my cash and phone and credit cards. She looked desperate, but I have no idea how to tell which was true.
I decided immediately that I had to help her. If she was telling the truth, she was in immediate physical danger. If she wanted to rob me, well, hey, it's only money. Luckily my friend was less of an idiot than me. Once she realised I was going to drive this stranger to the nearest station, she said she'd follow me. So, yeah, no risk at all. But if I left her there, and something had happened. I'd have never forgiven myself. I've been robbed, and it "only" took a year for me to get over it.
Bonus points if you can identify which rowing club based on the above information.