Do I need to meal prep to be successful?
No, but you need some form of food readiness. Meal prep is one way to reduce decision fatigue, prevent emergency eating, and make the default choice match the goal. It is not the only way.
You can prep full meals, batch-cook proteins, keep frozen options, use repeatable grocery lists, build simple plate templates, or keep convenience foods that fit your targets. The point is to make the next good meal easier than improvising under stress.
If meal prep makes your life easier, use it. If it creates dread, waste, or a fridge full of food you do not want to eat, simplify. The best preparation system is the one you will actually repeat.