Eating a plant-based diet does require some knowledge of nutrition for long-term health. Some people complain that they tried eating a plant-based diet and couldn't stay on it for health reasons. If essential nutrients are not included then eating a plant-based diet can lead to nutrient deficiencies. But the Standard American Diet is far more deficient. That's why it's called the SAD Diet. A lack of fresh fruits and vegetables leads to many illnesses down the road, although this can lead to a more gradual decline that is less noticeable until serious illness occurs.
Whatever diet you choose, be sure to include at least 80% plants in your diet for sufficient fiber, vitamins and minerals. A diet high in animal products is low in fiber, magnesium and many other essential nutrients.
There are specific nutrients that need to be included in a plant-based diet. A switch from hamburgers to vegan mac & cheese will not work long term.
One excellent source of many nutrients is beans. Some people find them to be hard to digest at first, but your body will learn to digest them well if you add fermented foods, prebiotics and probiotics. Also onions and carminative seasonings. Beans and legumes are high in fiber and greatly enhance digestion when eaten regularly (weekly or even daily).
A specific nutrient that some vegans and vegetarians need to focus on is iron. Black beans and beets are great sources of this important mineral. If you are prone to iron deficiency eat these foods at least once a week. Dark greens also. Other foods high in iron are sesame seeds, oats, and other beans and legumes such as lentils. A standard blood test will tell you if you are getting enough iron. If you feel tired, run down and sluggish, eat some beets or black beans and see if you feel better.