Forming a new habit is an upward spiral. 

We start off by doing something. We see a positive response in terms of how it makes us feel. And we repeat it the next day or the next week and are further reinforced. And we do this until it becomes the natural thing to do and becomes a part of our routine.

On the other hand, losing a habit is a downward spiral. 

We miss one day of reading, or working out. We don't see an immediate negative response to it. In fact, we may see a momentary positive response through freed up time or reduced effort. And we do this again until we realise it is too late and that we have already lost the habit and need to start over again to recover it. 

Downward spirals are the easiest to achieve. Upward spirals are hard. 

Downward spirals are the ones to watch out for.