The chain comprises multiple links that come together and connect perfectly. Only when they are all connected is it whole, and disconnecting just one link will make the entire chain ineffective.
The principle of building or breaking habits and behaviors is the same. It is one link at a time. For example, it is a day of refraining from being angry or upset with others, exercising, or possibly staying sober. If we start with one day and mark it as such, soon we will have two, three, and before we realize it, a month plus. Yet, it starts with the first. Once we start, we find all too well that it becomes easier to do, and ultimately it now becomes our new habit or behavior with little second thought. Do not fret when the pattern breaks since you can fix it, similar to the chain.
What chain do you seek to build? Start today and mark it on a calendar. Then, watch as the calendar begins to fill up. You will want the streak to continue, and not breaking it will become a priority.