With summer vacation over, we head back to work or school, to our normal routines. We begin the fall with a great sense of optimism about all we can accomplish. We vow to do things differently. Yet come Thanksgiving, we’ll find we didn’t get as much done as we thought we would. We procrastinated.

Everyone dawdles from time to time; it’s a universal trait. But not every procrastinator is the same.

Procrastination comes in two types. Some of us procrastinate in order to pursue restful activities — spending time in bed, watching TV — while others delay difficult or unpleasant tasks in favor of those that are more fun.

In this respect, the two types differ in activity level: The rest-seeking procrastinators would generally rather not exert themselves at all, while the fun-task procrastinators enjoy being busy and active all the time, but have a hard time starting things that are not so amusing.

The tendency to procrastinate has been linked to both genetics and the neurobiology of the brain. People are more likely to procrastinate if they are young and single (including divorced and separated). So are those with a Y chromosome, which could explain why women are far more likely to graduate from college than men.

Self-regulation and impulse-control problems in general are more likely to be found in males, who have a larger number of fatal and nonfatal accidents, a higher suicide rate, a higher incarceration rate and are more likely to seek and take risks. Variations in the structure of genes that regulate dopamine in the brain influence the extent to which we can control our attentional focus. One new study has shown that variations in a gene that regulates the neurotransmitter acetylcholine in turn affect our ability to experience a sense of reward.

And, as it happens, reward is an important part of the story of procrastination — for all of us. We tend to put off those things for which we will not get an immediate reward: projects with a long event horizon such as those undertaken by academics, engineers, writers, housing contractors and artists. The output of their work can take weeks, or months or sometimes years to complete. And then, after completion, there can be a very long period before they receive any praise or gratification. And so there is a very strong pull from the brain’s reward center to engage in something — anything — else that will deliver a more immediate sense of satisfaction. The Internet to the rescue!

The human brain long ago evolved a mechanism for rewarding us when we encountered new information: a little shot of dopamine in the brain each time we learned something new. Across evolutionary history, compulsively seeking information was adaptive behavior.

But a funny thing happened on the way to the 21st century. Whereas information came at us very slowly 1,000 years ago, now it comes faster than we can process it. We’ve created more information in the last five years than in all of human history before it. Each new Facebook post, Twitter feed or email is a bit of new information that causes our brains to release dopamine and to experience immediate, if fleeting, pleasure.

Getting new information through Web-surfing almost always feels more rewarding than having to generate new information in the work that is in front of us. It therefore takes increasing amounts of self-discipline to stay on task.

We can’t just blame evolution and dopamine, though; we make getting down to business more difficult than absolutely necessary by defining a task too broadly, with not enough detail. "Build a house" is not something you can easily start. But grading the site, preparing to pour a foundation and starting framing are executable steps that themselves can be broken into subcomponents such as hiring an excavator and setting stakes for the outline of the foundation.

Often our tendency to procrastinate is a nuisance and nothing more: We simply start things later than we might have and experience unneeded stress as the deadline looms. But it can lead to more serious outcomes. Many people, for example, delay seeing their doctors, during which time their condition can become so bad that treatment is no longer an option. Or they put off writing wills, filling out medical directives, installing smoke detectors or backing up their computers until it’s too late.

The keys to a productive fall season include prioritizing tasks, breaking down large tasks into smaller steps and undertaking unpleasant or difficult tasks early in the day (or after lunch or a nap). Also, exercising just a bit of self-restraint when it comes to social networking. Staying away from electronics for at least short stretches can create a state of focused and relaxed engagement, which some call "mindfulness."

The sheer volume of options that we face in this age of information overload nearly guarantees that we won’t finish everything. But when the December break comes, we may find that we’ve at least managed to finish (or at least start) the things we care about most.