Final answer:
The quote relates to a person's feelings of failure when they cannot sustain 'change' in their habits or behaviors.
Step-by-step explanation:
The quote 'Dark clouds of remorse and despondency will reign during the last week in January, but by February 1st you will have become accustomed and resigned to your old habits' suggests a person's feelings when they are unable to sustain change. This is because the context of the quote implies a sense of failure or return to old ways after an attempt to alter one's habits or behaviors. The emotional states of 'remorse' and 'despondency' are often associated with the failure of maintaining personal development or improvement efforts, such as breaking a bad habit or making a lifestyle change. Therefore, the most likely answer to fill in the blank is 'change'.