If you wear a watch (and most therapists do, since checking the time on your phone isn't really appropriate during a session!), try it for yourself. What do you notice?
Most people feel at least a little discomfort with this activity (and perhaps resistance), even though which wrist you wear your watch on has little actual importance or emotional significance. It's just a habit, based on social convention, which is based on the inconvenience of trying to wear a watch on your dominant arm. The fact that it still makes us uncomfortable to swap wrists highlights how very uncomfortable change really is.
Something about our neurological or psychological make-up makes us creatures of habit. In fact most creatures are habit-driven (if you don't believe me, pay attention to your pet's daily ritual). When our routine is disrupted, it provokes varying degrees of anxiety (depending on the significance of the disruption, our temperament, and other stressors), and we typically want things to go back to the way they were.
This is an important fact to keep in mind as we encourage our clients to change. Change is uncomfortable! It's uncomfortable when it's inconsequential, and it's downright painful when the change has deeper emotional significance.
Even when change is good, necessary, and desired by the client, it's still going to be uncomfortable. That means that it's quite understandable - normal, even - for a client to experience anxiety, resistance, avoidance, or reverse progress when attempting to make a change they have said they want. It's easy for therapists, and other supporters, to feel a little exasperated when we look only at the "facts:" my client says she wants to change, and then does the opposite! Why is s/he even coming to therapy if s/he doesn't really want help?
Instead, we are better therapists when we remember that change is always uncomfortable, and expect and empathize with the resulting difficulties our clients experience when they consider or attempt change.