Have you ever tried to get into a habit of doing something only to fail after a while? We've all fallen prey to temptation and what is often referred to a "lack of willpower or discipline".
On the other hand, the power of habits is extremely powerful. In fact, I believe that building something into a habit is the only true way to effect change long-term.
Gretchen Rubin, author of Better than Before, points out that the approach to building habits should be dependent on the type of character a person has. Not everyone responds to the same stimuli in order to build a habit.
For example, some people are "Abstainers" while others are "Moderators".
Abstainers are people who do best when they completely abstain from something. They're "all or nothing" type of people. Vegans are a good example of Abstainers. Such people don't respond well to an 80%/20% approach for example, as for them this could put them on a slippery slope.
Are you the kind of person who, for example, abstains from chocolate for 3 weeks, but then when you try to reward yourself for it by having "just a little", end up falling off the bandwagon and eating an entire box?
Or are you someone who frequently turns a "cheat meal day" into a "cheat meal week?
In that case, you're an "Abstainer". Recognize yourself as such, accept it, and seek to build successful habits in that context: you're either in or out, no halfway solutions.
Abstainers will have a harder time building discipline initially, but once they get past that initial phase, the temptations go away and they "live happily ever after".
What's ironic is that most of those who promote "everything in moderation" are Abstainers at heart, which is why they fail in developing sustainable habits.
"Moderators", on the other hand, have a different kind of self-control: they're able to put the "just this once" or "just a little bit" approach to good use, remaining in control of their impulses and maintaining the habit. These are individuals for whom the 80/20 rule actually works.
Moderators don't do well when abstaining completely from something: they become obsessed about it and can't think about anything else.
Now that I think about it, I recognize myself as a Moderator in certain areas and an Abstainer in others.
For example, I'm a Moderator when it comes to chocolate, ice cream, training: I can have chocolate or ice cream once every 2 weeks and not even think about them in the meantime. I can skip training for a day or 2 and get back to my routine with little effort.
On the other hand, I'm an Abstainer when it comes to gluten: once I eat gluten I find it hard to stop again (although this might also be due to the opiate-like addictive molecules in gluten).
Bottom line: if you're keen on building a sustainable habit, ask yourself if you're an Abstainer or a Moderator with respect to this particular aspect of your life, and build that habit accordingly.