Is it really possible to get all nutrition needs (vitamin and mineral etc) all from the food we eat alone ? i find it hard to believe it can be done.

Sure: It is possible, but for most of us it is difficult. We need to eat lots of fresh, high quality vegetables and fruit. We need healthy, whole grains and clean meat . We can certainly be healthy without meat, but it does require a bit more effort. We need to not eat empty calories in the form of alcohol and sugary snacks and pastries. It can be done, but it requires planning and effort.

Yes without habits.: Provided you have no food fads, no malabsorption issues in terms of gastrointestinal tract, taking the correct types of food - without junk foods, or monotonous food habits, but with properly varities of food in the right proportions , incluive of vegetarian and nonveg. Foods, fruits, nuts etc. With aging when we feel easily fatigued , vitamins for short periods like 3-6 months may help for stress.

Supplements: Yes, one can get all the vitamins and minerals they need just from diet alone. This is accomplished by maintaining a diet that his high in a variety of fruits and vegetables, lean proteins from different sources, low in saturated fats, high in unsaturated fats, and a variety of complex carbohydrates. Vitamins are like insurance, take them "just in case" you don't eat as recommended.