Time and again, I see a person who wants to get rid of a bad habit, say smoking. They are very determined to quit it in near future. They go from 10 cigarettes a day to 8 for some time and their plan is to continue decreasing this amount until it becomes zero. Very rarely the goal is actually achieved.
On the other hand, there are also people who are determined to develop a good habit, say exercise. They start strong, say by running 5 km in a day, continue for a short period of time before packing up everything and not finding enough time due to some upcoming busyness.
What I have noticed is that most people want to do away with a bad habit gradually over a period of time, while others want to develop a good habit overnight.
In my experience, the reverse is actually true. A bad habit needs to be quit once and forever, while a good habit needs to be developed gradually over a period of time.
Think about growing a tree. A tree starts as a seed, takes a lot of care and time before it can become a baby plant, and then another stage of development before it becomes a self-sustaining weather resilient force.
On the other hand, when it needs to be cut down, you have to do it in a single day. A person who strikes an axe on a tree once or twice a week before showing up next week is not going to cut it.
In conclusion, if you want to abandon a bad habit, today is the day. If you want to develop a good habit, start small, be consistent and let it grow.