The concept of chaining is to keep going with the changed habit for as long as possible. Each day you keep going the chain gets longer. If you stop a chain for whatever reason you should not feel guilty but start a new chain and focus on making it longer than the previous one.
It is a very simple idea and its power is on keeping you motivated instead of having bad feelings when you struggle within the process of changing a habit.
http://www.anextrahoureveryday.com/2008/08/23/focus-on-motivation-not-discipline/
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