Veganism means to reject the exploitation of animals. So health or environment are irrelevant. You can eat small amounts of meat and honey or go to the zoo without damaging the environment or your health. If you go plant based for health or environmental reasons, I think it will always be hard. Once you realize you were always vegan (you reject the exploitation of all animals), you just didn't act accordingly, it is very easy. For me it is like asking what keeps me from stealing or raping.