The transition was fairly easy for me.
I never really liked meat or dairy to begin with, so when I moved out to college I started buying way less of these foods. Since meat takes a while to cook and I was fairly lazy, it was a win-win. I ate chicken nuggets, sausage rolls, bacon in salads, ham in sandwiches, and meat in my pasta sauce. So I was still consuming some meat but way less than when living at home (every dinner had chicken, steak, pork chop, or something big and meat-based).
The next year I just wanted to eat healthy in general so I stopped eating the chicken nuggets and stuff and only had sliced ham for sandwiches and the meat in my pasta sauce. If eating out I would get an occasional burger.
Then I started reading about vegetarianism and all the health benefits (cancer is common in my family) and since I was almost there (5% of my foods were probably meat) I decided to just go all the way.
A couple months into this I began to feel really fatigued (I also ran 10 miles three times a week). So I started counting protein and realized I was REALLY low. I decided fish would be okay since of all the omega fats and such. I held this for a year and a half.
Two weeks ago I decided to switch to veganism, it randomly hit me like a brick wall that animals aren't food and that includes fish. Also I was eating fish every day which isn't good because of all the mercury and probably also because of the conditions farmed fish are in.
The past two weeks have been extremely easy, i've been eating mostly nuts and seeds and have a homemade granola that I absolutely love. Love lentils, tofu, hemp seeds, and mixed veggies thrown together in a salad as well! No protein deficiences this time since I am making smart choices and eating more variety.
When I failed last time I was literally eating the same foods every day: oatmeal, toast, fruits, spaghetti, and a salad or sandwich. Literally the exact same foods every day. So no wonder I was low in protein, especially since there were probably some amino acids I wasn't even receiving.