Back when personal computers first appeared in the early 1980s, you could do only one thing at a time. You could run a word processing program or a spreadsheet but not both at once. If you wanted to switch between them you had to save your work, completely exit the application, then start up another one.
Then in the mid 80s, something called "time-slicing" came along. A computer would hold several applications in memory and the CPU would divide up its time between them. It worked on one task then switched periodically to another, but it did it so quickly that it seemed like the programs were running simultaneously.
Multitasking was born.
Today, we take it for granted that we can open multiple applications, keep them running simultaneously and switch between them with a single click. You can now get multiple inputs at the same time: one window plays music while another shows you the latest news and you do your main work in a third.
People are also multitasking in their personal lives, assuming they can do things the same way computers do. There are more sources of stimulation than ever before, and people feel they need to do them all simultaneously or in rapid succession: computers, TVs, cellphones, iPods — not to mention all the endlessly replicating real-world tasks we find ourselves obligated to. Before personal computers, it was fashionable to say that humans used only 10% of their brain capacity. Now they are using 110%! That doesn't mean, however, that people are more productive or happier. The cost of quantity is quality.
The problem with multitasking on computers is that your PC can eventually become so cluttered with active tasks that it slows down and becomes unusable. This is true no matter how much processing power you have. Computers today have 1000s of times the CPU speed of computers in the 1980s, but when you crank up your word processor it may run so... incredibly... slow... that you almost wish for a nice simple one-task computer from the old days.
The really disturbing thing is that most of those processes slowing down your computer are junk tasks you don't really need and may not even be aware of. It could be a virus slowing down your computer or some unused application you installed long ago and forgot about. Personal computers today are a mess! In spite of any "optimizing" you may do, they are always compromised by irrelevent processes.
Likewise, people are undoubtedly busier than ever before, but most of those processes are junk tasks that don't really move your life forward. Of course there is the obvious cerebral junk food like video games and trash TV that soak up hours in a heartbeat, but junk can also come in appealing packages that don't seem like junk on the surface. It is hard to resist a five-star movie or an exciting vacation or a party with a lot of nice, interesting friends, but even this good stuff can be junk if there is too much of it.
Truth is, there is limit to how many apps your brain can run without the whole system getting fried.
CPUs in computers have their hardware limits. There is a maximum number of simple transactions you can force through them in a second, and once this limit is reached, you're going to have a systemic slowdown. People don't realize that human consciousness also has its hard limits. These parameters are much more difficult to define and measure, so it is easy to assume ones brainpower is unlimited, but there is a definite maximum-thoughts-per-minute and we find ourselves bumping up against it all the time.
We are all familiar with the problem of driving and cellphones. Studies show that drivers talking on phones are every bit as dangerous as drunk drivers. Governments respond by banning hand-held cellphone use, but speakerphones are almost as dangerous. The problem is not holding the phone but subdividing ones consciousness. A phone call, even a trivial one, is a high-priority brain task which pushes driving into the background. People run red lights and cut off others without even knowing it.
Whatever consciousness may be, it employs a form of time-slicing. It focuses on one task for a certain amount of time, then switches to another. The slice given to each task is measurable and significant, more in the range of seconds than milliseconds. Sometimes the switch between tasks is internally prompted—daydream thoughts that segue naturally from one idea to another—and sometimes it is triggered by an outside event. If you are driving on a straight road, your thoughts can wander for some time until something happens in front of you that snaps your attention back to the road. (That is, unless another more involving task gets in the way. )
It is no mystery that the more you slice up a pie, the less of it each person gets. If conscious thought is a limited commodity and you divide it among twenty tasks, each task will get, on average, one-twentieth of the attention. Inevitably, there are some tasks that monopolize more than their fair share of attention, and these aren't necessarily the most important ones. A trivial phone call while driving will kill you just as surely as an important one, because all calls take priority in consciousness.
Simple math says that the more you divide up quality thought, the less quality gets allocated to each task. "Quality" means devoting sufficient processing power to a task to do it well. When driving, quality is obvious, if you miss a red light and drive right through it or if you miss some other clue on the road like slick ice ahead, then the quality of processing is low, and you could die for it.
The same applies on the macro level. If you go from one hour-long activity to another and another with no gaps in-between, then you may have been focused fully on each task but you have had no time for any higher-level processing of the experience. You don't have time to regurgitate and reprocess, which is an essential part of learning. If you engage in an hour-long learning task, it is better to have a free hour to think about it afterwards. Then you have time to integrate and process what you have learned and you will probably do it better the next time than if you had no intervening thinking time.
In the modern world, it seems to be taken as a badge of honor to have a busy life full of involving activities from dawn to dusk, but what this often means is a trite and superficial life that isn't nearly as productive as it seems to be. The main goal in life is not to do a LOT of things but to do the RIGHT things, and this is where heavily multitasked people usually miss the boat. They have no time to think about what they doing, no time to ruminate on whether this is really the best path, so they can easy go off on unproductive tangents for years at a time.
Another thing you notice about overprogrammed people is that they are very passive. In other words, they will will respond to events around them but they rarely initiate them. Initiative takes time, thought and effort that these people just don't have. This makes the vulnerable to whatever stock solution someone else hands them, whether or not it it really right. In an unexpected crisis, multitask addicts may try to buy their way out of it instead of stopped to analyze the situation, which they don't have time for.
Overprogrammed people may be full of surface life, but don't expect a lot of deep interaction from them. They will respond to your questions but may not give much attention or care to their response. They may smile, but their mind is only half there. They may be full of promises but weak on follow-up. They are always racing to the next item on the agenda. If an unexpected issue, crisis or opportunity comes up, they can only devote to it the few available seconds between other activities.
Heavily multitasked people miss some of the best things in life because those events are not on their prepared agenda. When unexpected things happen, they just can't process them, let alone take advantage of them. Multitasked people aren't very curious about the world around them because they don't have time to be. Aliens could land on the front lawn, but they'd just shrug it off because they don't have time to investigate.
Computer technology has certainly come a long way since the 1980s, but it's not clear that our lives have gotten better for it. In the old days, you could still switch tasks—from word processor to spreadsheet—but there was a high cost of doing so, so you didn't do it very often. Now, it is a too easy to switch. Your time is sliced into ever-tinier bits, without much quality devoted to each. On the macro level, people are leading busy, superficial lives, blessed with a stunning variety of sensory input and no time to digest it.
You CAN get back to the 80s—back to the mythical age when people supposedly had time to think—but only through deliberate effort. You have to aggressively cut down your inputs and slough off obligations faster than you take them on. A 100% activity level isn't healthy for anyone. You have to be doing a lot less with your body before your mind can catch up and give meaning to what you do.
The thing most tragically lost in multitasking is the opportunity to think things through. You want to be taking MEANINGFUL actions in your life, not just busy ones.