[S]cience has consistently shown that the human brain can only sustain attention on one item at a time. Our overestimation of our attentional capacity stems from a fundamental misunderstanding of the concept of multitasking and of the human attentional system as a whole.
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The brain’s attentional system functions like a searchlight in a pitch black night. Whatever external or internal item we wish to focus on is illuminated by our attentional searchlight. Importantly, our neurological searchlight has limited wattage so any focal point that falls outside the radius of its beam is cloaked in darkness. When we wish to attend to another item in our external or internal environment we swing the neurological searchlight to the new item, and by the definition of our finite attentional capacity, lose the original item to the inky darkness that envelops our beam.
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As it turns out, far from being a shortcoming of the human brain, our inability to focus on more than one item at a time provides an inroad to mindful practice.
Thus, by practicing mindfulness we build an off ramp for the superhighway of worry, self-blame, and obsession. We will inevitably have to return to the highway of thought before long, but it is surprising what a little break can provide.