Have you ever played a game and forgotten the time? Psychologists call this feeling "flow." Flow often happens when three things are true. You have a clear goal.

You can see your results quickly. And the task is not too easy and not too hard. If it is too easy, you feel bored.

If it is too hard, you feel worried. One study even found that people felt flow more at work than in free time.

Flow is the state of being so absorbed in an activity that you lose track of time. The idea was developed by the psychologist Mihaly Csikszentmihalyi, who interviewed painters, rock climbers, and chess players. Flow tends to occur when goals are clear, feedback is immediate, and the challenge matches your skill. If a task is too easy, you get bored; if it is too hard, you become anxious.

In a 2008 experiment, people played a falling-block puzzle game at three levels. They felt most absorbed when the difficulty adjusted to their skill. Csikszentmihalyi also found something surprising. In a 1989 study, workers who recorded their activities several times a day experienced flow more often at work than during leisure, yet they often wished they were doing something else.

In 1989, researchers gave pagers to 78 working adults and beeped them at random moments for a week, asking each time how they felt. People reported flow, the deep absorption described by the psychologist Mihaly Csikszentmihalyi, more often at work than in their free time.

But while working, they often wished they were somewhere else, a pattern known as the "paradox of work." This describes a pattern but does not show that work causes flow. In flow, you lose track of time while painting, climbing or playing a game, and action and awareness seem to merge. Interviews with artists, athletes and chess players led Csikszentmihalyi to three conditions that make it more likely.

The goals are clear, feedback comes at once, and the task is about as hard as the person is skilled. Make it too easy and boredom sets in. Make it too hard and anxiety takes over. In a 2008 experiment by Keller and Bless, people played a falling-block puzzle game that was too easy, too hard, or matched to their ability. The matched version produced the most absorption and enjoyment. A 2015 meta-analysis confirmed the link, though its strength varied with the measure, culture and activity.