Good quality coffee will commonly have some bitter elements, but they should exist in balance with other aspects; bitterness should not be an overwhelming component. Unfortunately, most people are rarely served anything but poorly prepared coffee that may also have been sitting on a warming element for extended periods, so the standard experience is that coffee is bitter.
What if my coffee is too strong or too weak?
First, be certain that the problem is that your coffee is too strong or too weak. Often people will confuse “bitter” with being “strong.” If your coffee is unpleasantly bitter, one cause may be that your grind is too fine for the steeping duration; use a coarser grind. A lower-quality grinder will also produce a lot of dust, which will make the coffee taste bitter. If the coffee is too coarse for the brewing technique, your coffee will be under extracted; use a finer grind. Your coffee isn’t weak in the sense that the taste is diluted; it’s because many of the desirable flavor elements (which don’t all extract at the same time) are still in the grounds and simply never made it to your brew.
Some roasters over-roast their coffee as a matter of course, and the distinctive taste of charcoal may therefore cause the coffee to be labeled as strong. It isn’t: the roasted beans are defective. Or, the roaster may also have “baked” the coffee, which means that certain physical and chemical changes didn’t occur during roasting, and the coffee will taste flat no matter what you do. If your coffee beans are good, and the grind is appropriately fine for your brewing technique, then simply adjust the amount of coffee you use. If your grind is right, then you’ll be extracting a desirable profile of solubles from the grounds, just in different quantities.