Here’s an interesting quote from William Walker Atkinson:

“A habit is a “mental path” over which our actions have traveled for some time, each passing making the path a little deeper and a little wider. If you have to walk over a field or through a forest, you know how natural it is for you to choose the clearest path in preference to the less worn ones, and greatly in preference to stepping out across the field or through the woods and making a new path. And the line of mental action is precisely the same. It is movement along the lines of the least resistance—passage over the well-worn path.

Habits are created by repetition and are formed in accordance to a natural law, observable in all animate things and some would say in inanimate things as well. As an instance of the latter, it is pointed out that a piece of paper once folded in a certain manner will fold along the same lines the next time. And all users of sewing machines, or other delicate pieces of mechanism, know that as a machine or instrument is once “broken in” so will it tend to run thereafter.

The same law is also observable in the case of musical instruments. Clothing, or gloves form into creases according to the person using them, and these creases once formed will always be in effect, notwithstanding repeated pressings. Rivers and streams of water cut their courses through the land, and thereafter flow along the habit-course. The law is in operation everywhere.

The above illustrations will help you to form the idea of the nature of habit, and will aid you in forming new mental paths—new mental creases. And, remember this always—the best (and one might say the only) way in which old habits may be removed is to form new habits to counteract and replace the old undesirable ones.

Form new mental paths over which to travel, and the old ones will soon become less distinct and in time will practically fill up from disuse.

Every time you travel over the path of the desirable mental habit, you make the path deeper and wider, and make it so much easier to travel it thereafter. This mental path-making is a very important thing, and I cannot urge upon you too strongly the injunction to start to work making the desirable mental paths over which you wish to travel. Practice, practice, practice—be a good path-maker.”

Atkinson clearly explains here the nature of habits. And it’s also well explained why it’s often hard to create new habits.

The old habits are a path well traveled, it’s very easy to go down that path. To forge a new habit you need to create new pathways. Often by going through paths that are much harder and need to be established… but once they are created, then it’s smooth sailing from there.