Or, you're reading a paper and realize you've been staring at the same paragraph for about 4 minutes.
The phenomenon is known as mind wandering, and according to scientists you spend a large part of your life doing it.
"As much as 50% of daily cognition is spent on spontaneous cognition- basically daydreaming or mind wandering," says Dr. Scott Barry Kaufman, adjunct associate professor of psychology at New York University.
"It is a fundamentally human cognitive process that arises from our inner stream of consciousness."
Mind wandering happens when your mind stops being present and thinks about concerns unrelated to what you are doing. For this reason, it has traditionally been viewed as a cognitive waste of time, or a lack of mental control or ability.
But, that is a judgment scientists are now asking us to reconsider.
"Mind wandering seems to be very useful for planning and creative thought," says Dr. Jonathan Schooler, from the University of Santa Barbara in California's department of psychological and brain sciences.
"It seems that allowing people an incubation period in which to let their minds wander, really helps the creative process."
Kaufman agrees, "This is where things like problem solving, creativity, goal driven thought, future planning, seeing the perspective of another person, and so on - find space to exist."
For this reason, he says, there is great benefit to allowing people and employees time to reflect on a problem - get their mind away from it as well - and then reconvene.
"When you don't allow time to mind wander or make space for reflection, you are limiting your chances for making insights," he says.
"Aha moments don't come from a directed and particular focus on a task, but by letting your mind wander and open up to other possibilities."
Hey, where are you going?
The trouble with mind wandering is, of course, that it's got a mind of its own.
"Mind wandering can be very disruptive to accomplishing primary tasks," says Schooler, "and when reading, for example, it is a major obstacle to comprehension. "But if mind wandering is so disruptive, why do we do it so often?"
And where do we go? According to Dr. Malia Mason, professor of management at Columbia University, and former postdoctoral fellow in cognitive neuroscience at Harvard Medical School, your mind has a preferred destination -- what she calls a sort of VIP lounge of unresolved issues.
"One of the things I have been struck by is the frequency with which people's minds wander to things that are unresolved, or to what we might call open goal," she says.
An open goal might be a conversation with a friend, a task you have to finish, the laundry, or a delayed phone call. "But, it is a misconception to think wandering thoughts are random," she says.
The key to working with your wandering mind, is to keep unimportant clutter - such as household chores -out of the VIP lounge, so your mind can wander to unresolved things that are important. "Keep your mental radar as clear as possible," she says.
Schooler suggests identifying issues, problems, questions, that we like to think about - to help us naturally go to those issues when our mind wanders.
One company that seems to have recognized this is Google, he says, referring to their policy of allowing employees up to 20% of their time to a project of their choosing.
According to Google
, engineers are given a lot of flexibility to join projects that really excite them, and are encouraged to spend time on other projects around the company, that interest them - typically known as 20% projects.
They tell CNN that this sort of innovation is a critical driver in their development of innovative ideas and products. And, it is core to their culture, because they recognize people are more productive when engaged in things that interest them.
This is also in line with Kaufman's experience, which is that we can direct our minds with such things as mental simulation of goals, problems, and tasks at hand.
"Positive constructive daydreaming is important, so you don't lose it on aimless wandering," he says. "If you don't take into account where peoples natural stream of thoughts go, then there is an awful lot of brain power we are missing out on."
Still with me?
If not, you might consider a daily meditation
"What we found is that mindfulness meditation - 10 min per day- can significantly reduce mind wandering and increase reading comprehension," says Schooler.
"Meditation and mindfulness, an area that was marginalized - is now becoming recognized as having deep insights into how to maximize our mental efficiency."
Mind wandering is in a lot of ways what makes each of us individual and gives us our own unique personal character," says Kaufman.
"Without our ability to turn our attention inward and daydream, we are really not making personal meaning of our environment- and we are limiting our capacity for personal reflection and identity reflection. It would limit our attention."