It takes 21 days for the brain neurons to take root.
21 days of repetition.
21 days of doing the same thing over and over.
21 days to have the brain train a new pathway
Imagine emerging from a forest and in front of you is a field of tall grass that no one has ever walked in. You start to pick your way carefully across the field as the grass is as high as your elbows. You lightly stroke the grass as you walk through it. As you look behind you to see where you had come from, it is as if no one had ever walked through before. You cannot see your footprints behind you; the grass is swaying in the wind just as it was before you had entered the field.
The next day you take the same route and go through the field of grass again. Again, you stroke the grass as you walk through it to the other side of the meadow. You repeat this path for a few days and on this day when you look behind you, you notice that you can start to see the path your feet are making on the tall grass. A few sprouts of grass have been broken and are now bent over where you had walked on them.
You continue to walk this same path for the next week and each day the path becomes more and more visible of where you have been each day. By the end of this next week there is a clear path marked by broken blades of grass that have started to decay.
As the days go by the path becomes worn down and the dirt and rocks below the grass starts to show through. The dirt becomes compacted and the path becomes a trail that is getting wider and wider with each new day of your same journey.
It did not take long for you to create a new pathway to be groomed into an easy walkway. It would take many months for the grass to grow back if you stopped today from walking on the hard dirt.
Your brain neuron pathways are similar to the grassy meadow, it takes a bit for the path to be developed but once it is it is there and the more you continue on the same path the more solid and concrete the impression makes.
Be it known, it is also that hard to break a habit, stop doing what just comes subconsciously to you. Either way you have a choice each and every day to take the same path or create a new one.