I had eaten meat all my life up to January 1981 without giving it a thought. (I was born in 1955). Then, one evening, I saw a documentary about factory farming. It had scenes of pigs being kept in narrow cages, chickens being crowded together in thousands in limited space and having their beaks sliced off with hotplates to stop them from fighting each other, etc. etc.
I stopped eating meat the following day. Eleven years later, in 1992, I found out that most male chicks on free range egg farms were disposed of by gassing, and that cows were injected with hormone to increase their milk production. As a result, I gave up animal products altogether and have been vegan for the last twenty-one years.
I have only accidentally eaten meat about two or three times in the last 31 years. I bought what I thought was a vegetarian samosa once and only realised after eating a bit of it that it was a meat one, and about two years ago, I ordered what I thought was a vegetarian dish in a Spanish restaurant , and I simply forgot that Chorizo, one of the ingredients, was chopped up sausage. That was down to my own carelessness/sloppiness.
I am not dogmatic about vegetarianism/veganism; we humans evolved as omnivorous animals, eating meat which we either hunted or obtained from carrion, (carcases) or foraging for roots and shoots There are some theories that our brains became larger at some stage of our evolution because of protein from meat, but that makes no difference to me, I know that I will never knowingly consume animal products again.