I have been afraid of dogs nearly my entire life; when I was about 5 years old, (a very long time ago) a big German Shepherd chased me on my way to school and I had to hide between a tree and a fence to get away from him. Since that experience, I have been so afraid of dogs that I would cross the street if someone with a dog (on a leash) was walking towards me on the sidewalk.
Gradually I got to know some dogs (it seemed most of my friends owned dogs) and I grew to realize that some were gentle and kind (just like people). I finally progressed past my fear enough to pet a dog after I had known her for a few months. Eventually I even got comfortable enough to befriend a great Dane (who weighed as much as I do); he used to sit on me to show his affection for me.
Today I may still be a bit reserved when meeting a dog, but I allow my senses to tell me whether he is friendly or aggressive instead of automatically assuming he will try to bite me. It's been a long process, but I've met some wonderful dogs along the way who have taught me that my first experience is not the only experience possible. I got "dog therapy" from the calm and friendly dogs who taught me through their presence how to trust a dog.
I learned today that there are Therapy Dogs who go to disaster sites, nursing homes, and childcare facilities to help with the emotional, physical, and social well being of people; they bring joy and love to people who either can not receive it from other people, or don't receive enough of it from other people.
Dogs are wonderful healers and teachers, after all, it was the kind and gentle dogs of my friends who have taught me how to overcome my fear of the one who chased me decades ago.