10 years ago, I used to train and compete Brazilian Jiu Jitsu, I was trying a lot of diets and when I started yoga at the moment I decided to try being vegetarian, I felt good and watch a couple of documentaries and decided to drop meat (and alcohol), didn't even think about being vegan because I felt it was too extreme and no idea what I was going to eat. I'm originally from Argentina, on of the countries with more meat consumption per capita, I didn't know anyone vegetarian, less alone vegan.
After 5 years from that (5 years ago), I started running and was going to run my first marathon and decided to drop dairy, then I read Veganuary book, Eat & Run from Scott Jurek and Finding Ultra from Rich Roll and decided to try vegan. Once I made the connection there was no way back.
Becoming both vegetarian and then vegan, for me, started on health/sports performance, but I definitely now do it 100% for the animals.