Q. I've been working on a big project for a long time. Although I try to move ahead every day, sometimes I have to force myself to accomplish even a small task. When I skip a day, I feel guilty. How can I stay motivated?"

A. When you're working on a book, job search, business start-up, dissertation, or special project, you can feel consumed by the project. And often you feel as though you can't afford to take a break, let alone a day off.

I once heard a writer say, "Sometimes I'm really productive. I write five pages on my book! Then the next day I'm drained. So I review what I've written or organize my research files."

And I feel the same way. I resist taking a day off to read a new mystery, go for a hike, visit an art museum, or watch a season of an HBO series on DVD. But the next day, invariably, I wake up eager to work. And I accomplish everything I need to do, and more.

Frankly, I've never found staring at a blank screen (or paper, in the old days) does much good. Resistance means, "Time for a change of pace!"

These beliefs are supported by scientific evidence. Psychologists who study these up-and-down activity blips have found a certain randomness operates in human productivity levels.

For example, an employee "Bill" varied his arrival time at work. When Bill was late, his boss yelled at him. When Bill was on time, the boss offered praise.

Sure enough, Bill responded. The day after the boss yelled, Bill was on time. And the day after the reward, Bill slacked off and arrived late. So, concluded the boss, praise doesn't work. And punishment does.

There was only one problem. A computer demonstrated that Bill's arrival times showed a pattern of random variation. In fact, the computer could predict quite accurately how Bill would perform - with or without praise and blame.

The same pattern has been found among students: some days you learn faster while other days you just don't get it. And some days you're productive and efficient, while other days you're sluggish.

If you've studied statistics, you're probably guessed that we're talking about regression to the mean, which is very powerful. People usually have an average level of productivity. When they work hard one day, they tend to slow down the next.

So here's an exercise. Suppose you have a writing project. You set a goal: write 500 words a day. For other projects, find a daily activity level that's easy to observe and measure.

For the next 30 days, track how many words you write (or how productive you are in the task you've chosen). Some days you'll write 1000 words, other days none, with lots of variation. Each day just record your word count, without judging your output. At the end of 30 days, calculate an average. And calculate again after 60 days.

You may find that your natural average is 300 words a day. You can lower your daily goals - or recognize that you work best with your random pattern.

Obviously, if you have a deadline, you may have to increase your output. Professional writers typically write 1000-3000 words a day.

But if you're making acceptable progress toward a goal, you can begin to understand, accept and work with your natural rhythm. Regardless, beating yourself up and feeling guilty won't work. If you're constantly falling behind, maybe it's time for a change of career - a chance to enjoy marching your life to a new beat.

Most of all, I ask my clients to remove the word lazy from their vocabularies - forever! When you're berating yourself for lack of progress - stop! Chances are you're right on schedule.