Okay, here's my life story.
One week this summer I didn't bother to cook any meat because it was hot out and I didn't want to heat up the house. Instead, I lived off of my old standby, "poverty pilaf" (1-pot mujadara without caramelizing the onions.)
I just happened to watch "Forks over Knives", which documents all of the diseases associated with a modern western diet and advocates a "whole foods, plant-based diet" as a way of fixing them.
I considered the evidence pretty strong. With that, and the fact that I'd already lived a week without meat, I figured it wouldn't be too much of a stretch to go vegan.
Shortly thereafter, I moved back home from my summer job and restocked my pantry without any animal products. I bought FoK's cookbook, The Veganomicon, and Vegan with a Vengeance, and I haven't looked back since.
Since my reasons are primarily health-based, I'm not militantly-strict about my diet. I make four exceptions I call 'The four F's:"
To elaborate:
I have not yet "come out" to my family yet. I grew up on a grain and livestock farm in the middle of nowhere. The family hobby is raising, showing, and eating sheep. All of my family friends farm, hunt, and fish. We get half a beef every year from our closest friends. My mom was a dairy farmer, and she went to school to be a Home Ec teacher. It would be easier to be gay.
Friends. I don't have many, and I'd rather not be a burden to the few that I have. I'm not going to put up a hissy fit if we go to a bacon festival or get milkshakes.
I'm a poor college student. If a company or a club brings free pizza, you bet your ass I'm eating it.
I live in the middle of goddamn Ohio. While there's restaurants with vegan options in the bubbling metropolis of Columbus, if I go home, it's fast food an steakhouses as far as the eye can see, and I can't always cook all of my meals.
TL;DR: Laziness, frugality, and Forks over Knives. I'm not strict and make a lot of exceptions.