The first is that Veganism is a way of life, it is not a diet. Diets come and go; they are seldom adhered to, are rarely effective in the long term and infrequently create happiness. Veganism is for ever, it works on good health, longevity and on establishing a good body weight. For all of the above reasons vegans avoid eating anything with animal protein or fat in it. If they are clever they will also sidestep processed foods including vegetable oils. It is happy a way of life.
The second is one’s Veganism must be 100% in order to achieve good health and longevity. 80% vegan is easy, but ineffective. 100% Veganism does not guarantee perfect health nor immortality, but the 100% vegan is fully confident that everything is being done to achieve death from old age.
I don’t imagine one can successfully be a partial Christian, Muslim, Teetotaller, Non-smoker or any other selected way of life and the same is true of Veganism. I would suggest that of all choices of ways of life, Veganism will guarantee you the greatest tenancy to a cheerfully long life.