I'm Vegan (3+ years).
I can say that honestly. I have not willingly or knowingly eaten anything
of animal origin in that time. A lot of vegans struggle and shift in an out
of veganism, partly for social (family) reasons, partly because they still
subject themselves to advertising where meat, dairy and eggs are prominent (Television, mostly) and partly because
(especially if they are new) - they fail to get enough nutrition (a heavy reliance on stripped and manufactured foods that are lacking in fiber, vitamins, minerals and aminos.)
I went Vegan after a lifelong journey brought me there, struggling with
various ailments due to daily meat eating and learning a whole lot about
the disease connection to meat and dairy. Later, religious reasons applied
as I discovered them.
Just a word about soy. It's not required. I sometimes eat it, but one can
get all the nutrition one needs from other legumes, whole grains, fruit,
vegetables and seeds and nuts.
Personally, I've found processed vegan foods (especially those made to look
like commercial meat products), lacking. I've tried, for instance, Vegan
"chikin" nuggets - and although tasty, I basically had to eat the whole
box to feel satisfied. I also think they are a poor transitioning food...
primarily because they don't cultivate the gut bacteria vegans depend on,
which feed primarily on fiber, not textured high protein mock meats.
B12 - I don't supplement, although I do occasionally eat Vegemite fortified
with this vitamin. I am also careful to de-Chlorinate my drinking water, as
Chlorine kills the bacteria in the gut responsible for B-12 production. This is done by setting it out in the sun for a day.