The fitness industry and mainstream media are fixated on weight and, as a result, so is the average gym-goer. This makes sense from the fitness industry's point of view: weight loss or gain is an extremely easy metric to track, and since the average American is overweight, marketing your gym or program or product as a weight-loss tool is a good way to make it attractive to a lot of people.
For the average gym-goer, however, weight should not be the primary measure of progress towards "fitness" or "health." Here's why:
Other indicators are more important.
Measures such as body-fat percentage, blood pressure, and your lipid profile (cholesterol and triglyceride levels) are all more important to overall health and wellness than bodyweight and, like bodyweight, they can all be impacted positively by exercise. They're not as heavily emphasized in the fitness industry or the media for the simple reason that they're harder to track. You need calipers or a hydrostatic scale to estimate body-fat percentage, one of those arm-squeezing devices and a stethoscope to measure blood pressure, and a blood test to assess your lipid profile.
Weight and body composition aren't the same thing.
When people say they want to lose weight, they usually mean that they want to lose fat. In fact, many people think that losing weight and losing fat are the same thing. This is NOT true. If you lose fat, you will also lose weight, but it is possible (especially for men) that eating better and exercising will lead to fat loss AND weight gain. This is because exercise builds muscle, which weighs more than fat.
Which would you prefer?
Also, you can lose weight without losing any fat at all. Some fad diets and diet pills have the single effect of dehydrating you, leading to the loss of "water weight," but absolutely no reduction in fat levels or body-fat percentage.
Weight loss doesn't move you towards a specific fitness goal.
If you're obese, you need to get rid of some of your excess fat in order to be healthy. But "losing 20 pounds" isn't really anyone's fitness goal. Someone might SAY that losing weight is his or her goal, but if you press further, you'll discover that his or her real goal is to be able to walk up the stairs to the apartment without getting out of breath, or to look great in that wedding dress, or to have "six pack" abs. Losing fat might be a step towards achieving these goals, but weight loss for the sake of weight loss is useless and can be extremely unhealthy.
So I say to you, step away from the scale. Instead of focusing on how much weight you've gained or lost this week, focus on how your clothes fit and on your energy level throughout the day. Instead of setting your goal as "losing 5 pounds," aim to shave 10 seconds off of your time on the 1-mile run or add 5 pounds to your Squat. Ignoring the scale and instead concentrating on other measures of fitness and health will have a beneficial long-term effect on your health, and will, ironically, make it easier to lose that fat.