What events or experiences have made you disappointed in human nature for an instant?

I got lost and a runner with a dog passed by. I stopped her and asked her how to get to the park. She told me for a long time not to have any problems, and then she said goodbye happily. I kept walking and she kept running. Then I walked for a while and saw her running back. She said she didn't trust me and wanted to take me. At that time, even dogs were very enthusiastic about me. My heart is super warm. One year my wife and I went to Sichuan to play and came to Mianyang. I couldn't get a taxi, so I took a bus. When I got on the bus, I found there was no change, only a hundred-dollar bill, and the bus had already left. It's embarrassing. At this time, the uncle behind me paid the fare for us. He doesn't understand Sichuan dialect, which generally means that it is always difficult to go out. I was moved by this move. My uncle is sure that he doesn't have much money and he is carrying a basket. He may be a farmer, simple and generous. With such folk customs, the city must be warm, so he spent hundreds of thousands to buy a house in Mianyang. When I first came to Edinburgh to study, life was hard. Depression and anxiety fill my life. It was difficult to get up early for class that day. Before I left, I looked at the trash can that my roommate had left in the kitchen. After a while, I put on my gloves and packed up. I went downstairs with my leaking ass in one hand and the garbage bag mouth in the other. Standing in front of the trash can, I'm worried about how to throw this 20L garbage bag in. A hand came from behind to help me lift the heavy trash can lid. I don't look back, while busy saying thank you, while forcibly lifting the garbage bag and pushing it in. When I washed my hands and put my schoolbag back, I only saw the back of the man who just helped me. Even so, I recognized him: he was a beggar on the bridge where I had to go to school, and I bought canned food for his cat. He just walked ahead with a tattered canvas backpack with its original color washed away and wrapped in a dark red blanket. It suddenly occurred to me at that moment. Life is so hard, I still have the heart to help others. His light of humanity is much brighter than mine.