Years ago, my husband and I went on a road trip to Yellowstone National Park. While hiking in the back country, we found a lovely rock face that was just begging to be climbed. It seemed sturdy enough. There didn't appear to be loose rocks or boulders, and it wasn't exceptionally steep. So we started our ascent, looking forward to the view from above.
We had free climbed in similar situations many times without incident. However, this time, about 40 feet from the ground, I slipped. In a desperate attempt to prevent free-falling to my death, I fought with everything I had to grasp the side of the mountain. Luckily I succeeded, though I scraped most of my fingernails almost completely off.
That was it for me. No more climbing. In fact, I now give pause anytime I have to use a ladder. I never used to be afraid of heights, but I am now. I do not like to be on tall bridges, or look out the window of tall buildings. I get very nervous flying. I know that some of my fears are irrational, but I can't help it. I had one bad experience and now it seems it will affect me for the rest of my life.
This is why everyone should be cautious and deliberate with socializing their dog. One bad experience can affect your dog for the rest of their life, too. Whether it's a bad experience with a child, another dog, a man in a hat..... If they have a bad experience it's possible they may never recover from it. That one time, that one experience, may require training and maintenance for the life of the dog.