Consider the variability in what and how much we eat throughout our lives. Can we confidently say that we always choose healthy food?

Can we say that we eat the proper amount of food?

If we need to eat 2,000 calories daily to get our nutrition and we are only burning 1,800 calories, we will gain weight. On the other hand, if we eat only 1,8000 calories and maintain our weight we won't get enough nutrition.

If we are training for a sport and need 4,000 calories daily, we can probably get enough nutrition, but that too is a special circumstance that may require extra protein and iron for your best performance.

What about the food we eat and where it is grown? Is the soil depleted? Does your food contain as much nutrition as food grown on rich soil?

Also, consider different needs due to medications. Did you know antacids reduce your absorption of minerals? Cholesterol medications increase your need for CoQ10; diuretics can increase or decrease your needs for various salts. Antibiotic use can disrupt the gut flora which can then reduce your available B vitamins.

Supplements are prescribed for many people who are in at-risk groups like growing children, women of child-bearing age, during pregnancy, and elderly/less active individuals. 

But let's be honest... Unless you are hyper focused on your diet, food sourcing, well versed in pharmaceutical interactions and biochemistry...

You probably need to fill in nutritional gaps with a good Multivitamin.