Balance is what separates a well-made wine from a mediocre one. No single element — acidity, tannin, alcohol, sweetness, or fruit — should dominate at the expense of the others. In a balanced wine the components support each other: acidity lifts the fruit, tannins provide structure, alcohol provides body, and any sweetness rounds out the whole.
An unbalanced wine may be too acidic (sharp and piercing), too tannic (hard, bitter), too alcoholic (burning), or too sweet (heavy, tiring). Balance is not the same as a lack of character — a wine can be intense and powerful and still be in perfect balance. It is precisely this complexity that makes wine a craft art form.