Most of the habits that we try to introduce into our lives, and fail to introduce successfully, share a certain trait: The habit is hard to do in the beginning, but gradually gets easier to perform. The habit has become truly deeply ingrained not until the hardness of performing it is negative – when you enjoy performing it and feel a certain addiction towards performing it. This can be summarized in a curve.
On the Y axis is effort, or hardness of keeping up the habit. Usually our bodies and minds resist new habits, especially if they require us to spend more energy than before (like starting to work out, or to clean the apartment once a week). The effort even goes up slightly in the beginning before starting to descend. This is where most of us give up, because we cannot stand the thought of continuing to put in this much effort to keep up the habit. But over time, if you persist with a habit, gradually the effort to keep it up decreases.
For most habits, this happens over a few weeks. But I have noted that this can vary a lot. For example, my habit of regular physical exercise probably took around three years to really reach the point where I truly enjoy it every time.
The first time I began to understand that there is such a curve was when reading Mastery many years ago (which I remember as a great book on the forming of long term habits).
The rest of my understanding of the habit/effort curve has come through many years of trial and error trying to introduce new habits. Nowadays I think it is much easier for me to introduce a new habit, thanks to my understanding of this curve. If I recognize that it will inevitably be hard and require energy and effort during the first few weeks, I am much more willing to put in that effort, knowing that one day I will actually enjoy the habit.
Of course, since we exist in the real world, there is some more complexity involved. For example, some habits you will never enjoy, because they are simply wrong for you. And picking the habits that are the right ones for you is another blog post (or probably more like a whole book :)