I advocate making continuous improvement part of your daily / weekly work life. This I think should be something that most businesses should work towards if they aren't there already.
However, there are also times when things don't pan out quite as we have hoped to. Unfortunate circumstances, conflict inside the business or unforeseen problems. These take time away from the business and naturally makes it difficult to undertake continuous improvement activity.
There are other times when energies are higher. There are other events that can affect the motivation of your staff and this too can be considered.
So, the ebb and flow of the business can be mimicked by your continuous improvement projects. Sometimes you can be firing on all cylinders, and other times you may just be doing enough to keep things moving along. Continuous improvement doesn't have to be delivered at one speed.
There are two important principles at work here:
1 - Keep making progress, however fast that may be.
2 - Don't drop the habit, make sure that you can keep it ticking over until the time is right.
Author of 'Business Process Re-Engineering', a practical plan to improve business performance.