It is known that the fewer the days of vacation, the better one works and studies, because days are lost both before and after each day of vacation.
One would think that a person who rests for several days would then be full of energy, but as a rule he is actually more tired than he was before his vacation.
The change of pace is debilitating.
In this respect, completely ordinary days would seem to be better days.
On such days, a person can develop a routine that brings about gradual progress, step by step.
Their drawback, however, is that they offer the person no way of arriving at a critique of his habitual patterns of behavior.
The monotonous repetition of day after day after day prevents one from attaining the kind of awareness that the Sabbath brings to the week or that the festivals bring to the year.
In other words, festivals and Sabbaths are not just times of uplift.
Rather, they meet the need to break up the course of time so as to understand and to feel what it is that we are actually lacking.
–Rabbi Adin Steinsaltz