Once you have changed a pattern, change can come more quickly and easily.
I was thinking, as I opened this post, about how I had missed a day after blogging everyday for some forty days in a row, and how only two days later I missed posting again. When we're trying to create a habit that is challenging--for example writing something on our dissertation or other writing project everyday--and we fail to maintain a high standard we have kept for ourselves (or at least a standard that is strict, like to do something every day)--it then becomes easy to let it slip. Once the gates of "It's OK that I didn't do it" have been opened, they are hard to close again. Harder, perhaps, because the strict purity we had sought has been violated, and once violated, purity is hard to find recover.
It is, I think, a losing state of mind to let the lost purity keep you from the continued striving. Or maybe that's better stated that the focus on the lost purity itself is the cause of giving up the effort. It becomes the excuse for failure. It's easier, on some levels, to spend your time blaming yourself for the lost purity and lamenting it, than it is to get moving again.
But if you let the little failures keep you from pushing forward, then how difficult it is to find success! After all, is it not crucial for success that you press on? I wonder whether the difference between long-term success and long-term failure is nothing more than the response to the minor setbacks along the way.