Changing a behavior that has developed over many years isn’t going to be easily changed overnight. Anyone who has owned a new puppy or trained a dog knows that consistency is key in shaping behavior. In dog training and in human life, this means doing the same things and enforcing the same rules over and over. While this may seem like a simple concept, in real life it can be a bit more challenging. To train a dog not to get on the couch, you need to direct the dog by telling him "no" followed by redirecting him to a new spot, such as a dog bed. This needs to be done every single time he tries to get on the sofa.
We can relate the dog-training example to any health behavior you want to change, like quitting smoking or trying to start an exercise routine. If you plan to go to the gym four days a week, then you have to go four days a week. This sounds simple, but things come up and it’s easy to skip a day, then fall off track. While we all know what needs to be done, actually doing it consistently can be a daunting task. Consistency is about working on a larger timescale than just weeks and months. This builds up long time momentum and leads to sustainable behavior. If you run four days a week for several years, it becomes abnormal "not to run".
Any new behavior can be more difficult in the short-term, when just getting started. Doing something everyday is much easier than doing it just once in a while. The new behavior will become a new habit and part of your life.
"Habits are at first cobwebs, then cables." Spanish Proverb