Actually if you are a person who does well on a vegetarian diet at all (not everyone does, unlike what the dietician extremists and cloudeyed hippies would like to tell you. I tried it according to the guidelines and I did well on it for a while but eventually not so much.) then doing it well isn't all that hard.
Ovo-lacto-vegetarians eat dairy and eggs but no meat and no fish. Getting all the neccessary nutrients in this case is super easy tbh.
Any diet requires its research, but it's the vegan diet that is actually hard and can truly do extreme harm if not done according to recommendation.
Here are some things that can happen if a vegan doesn't consume vitamin B12 supplements or products fortified with the nutrient:
Weakness, tiredness, or lightheadedness
Heart palpitations and shortness of breath
Pale skin
A smooth tongue
Constipation, diarrhea, loss of appetite, or gas
Nerve problems like numbness or tingling, muscle weakness, and problems walking
Vision loss
Mental problems like depression, memory loss, or behavioral changes
Sometimes people display extreme behavioral changes and everyone thinks they've gone mentally insane... until they get medically checked and it's revealed they're low on vitamin B12.