This is a question with many different answers. Most of the time, people cannot answer this themselves. It takes deep thought, and often an outsider to help people recognize these barriers. Here are a few common barriers to reaching your fitness potential.
Lack of support from family and friends: If you are looking to eat healthy and exercise more, you need a support system. Motivation is tough to come by when surrounded by people that eat junk food and do not exercise. Worse yet, they may even give you a hard time for going against their norm. Join a group class or find a workout partner to help you stay on track when others attempt to derail you.
Lack of knowledge: Many people simply don't know they aren't living a healthy life. You can be skinny, yet still be fat. Having a bit of a belly is fairly normal. Functioning “fine” in life is not functioning optimally. It is imperative to learn about the benefits eating healthy and exercise. Understand your body better so you can begin making positive changes.
Fear of failure: If you are horribly weak, severely overweight, or simply lose your breath quickly during physical activity, you may feel you cannot improve your fitness. You have too much work to do and are unable to do what is needed. This belief is completely false. Yes, getting in better shape will be difficult, and slow at times. Fortunately, small increases in fitness can have profound positive effects. According to WebMD, for some, a two percent decrease in body weight is enough to notice health benefits.
Past failures: Past failures often hold people back. Fad diets, bogus pieces of workout equipment, and programs claiming six minutes a day to weight loss are huge reasons for these past failures. Seek out a trainer and/or dietician or nutritionist to give you useful information. Sleeping better, reduced pain, and looser clothes are all signs of progress, regardless of what the scale says. Focus on these changes to stay motivated.
False beliefs about exercise: You do not need to be athletic or spend a ton of time in the gym. Ladies, you will not bulk up lifting heavier weights. Walking for a half hour outside is enough to get the ball rolling. In the gym, do what your body can safely handle while still being challenged. Don't over think things.