You bring up a good point Doc, which is that the simpler the habit, the easier it is to form and the less effort. Perhaps simple is not quite the right word, as eating less is simple, but very difficult! But an easy physical action would be easier to forge, and much faster to establish so it becomes effortless.
In a Bayesian manner, I would also like to modify my insight with a further nuance. You have two behaviours: A or B. Press down the door lock, or use the remote. Each has its own level of difficulty. While you are trying to forge habit B, the cognitive effort required for B is more than the cognitive effort required for A. You have to think about doing it. However, after a while, there comes a tipping point where it is easier to do B than A. This then becomes your default choice, and with further repetition it continues to get easier and automatic.
Perhaps this is slightly different from the habit of going to the gym, because the gym itself will always require a large exertion of effort.
In any case, learning how to form habits effectively will give anyone an advantage over not knowing.