Because you don’t really want to change.
Ouch. If that hurt, then it is probably true. So often we make a couple of mistakes when setting New Year’s resolutions. Either:
1. The resolution is too vague, therefore making it feel overwhelming and unattainable;
2. We make a resolution surrounding something that we think we should change, but don’t actually want to change.
Addressing #2, ask yourself why you think you should make that change in your life. What is the outcome for which you are hoping? Then take the part that you do want and create steps to get there.
For example, if your resolution is to exercise every day, but you are currently exercising very little or not at all, then you probably don’t really like or want to exercise. But if you ask yourself the outcome that you would like, it is probably to lose weight, feel better, sleep better, etc. With those goals in mind, ask yourself what type of movement you do like to do. Perhaps you have always thought of “exercise” as running a few miles (but you hate to run), or taking a class at a gym (but you prefer to exercise alone). But maybe you love to play tennis, or dance, or would be willing to walk if you had company or a fun podcast to listen to. Perfect! Plan your resolution around one of those things that you actually have a likelihood of doing, and wrap it in some specifics.
Which leads me to #1. Vague resolutions tend to achieve vague results. Perhaps your resolution is to eat better in 2018. Think of specific steps that you could take (that are attainable for you) to make better food choices. For example, decide to pack a healthy sandwich or salad every day for lunch instead of going out to eat; resolve to buy one new fruit and one new vegetable each week at the store and add it to your meals or snacks; decide to cut down on soda intake by X amount; spend one evening each week looking up healthy recipes online. Simple but specific goals are much less likely to feel overwhelming and unattainable.
If you are having a hard time determining how to move away from a “should” resolution and on to a “want to” resolution, talk with a friend and have them brainstorm with you. Sometimes others have a better perspective on our habits and inclinations than we do. Ask them what they think you really want in your life and what they perceive to be your greatest obstacles. Then go from there. I am sure that you can find a more successful path to the goals that you truly desire!