Wine has to be in balance. There's a lot of combinations that will make for a balanced wine, but what does that mean. Emile Peynaud's The Taste of Wine
In a nut shell a balanced wine follows the equation:
Acidity + Tannin => Sugar + Alcohol.
There are a few corollaries that result from this equation. Namely that if there is a lot of tannin in the wine, there shouldn't be a lot of acidity, and it certainly needs to be offset by either sugar or a good dose of alcohol. Why alcohol? I'm so glad you asked. :)
Alcohol has an apparent sweetness to the palate. Most people don't realize it but it's true. The easiest way to prove this (if you're either a real go-getter or the scientific type or both) is to set up this little experiment. Boil the alocohol out of glass of wine. Run it through glass tubing and into a beaker. When all the alcohol has boiled out replace the same amount of water into the wine as the amount of alcohol that came out. The result: the wine will be unbearably bitter, either too tannic or too acidic or both. That's because when the alcohol is in the wine, it's apparent sweetness balances the wine. Without it, the wine is plonk.
Many people criticise California wines for being too alcoholic, and it's true that some are. But in the best California wines, elevated alcohol can still make for a balanced wine - all you need is the appropriate level of tannin or acidity to work in concert with it. Conversely, if there's a lot of tannin in the wine (something that will happen naturally when it's warm out because the skins of the grapes thicken and that's where the tannin is), the wine requires high alcohol, or else it will become to tough to drink - a problem that occurred in the heat wave of 2003 in France - the very problem that tainted my experience with Faiveley's Bourgogne. It's all about the balance.