Final answer:
Inattention is most commonly caused by focusing on multiple tasks simultaneously, known as inattentional blindness, where attention is so absorbed by one task that other stimuli are missed.
Step-by-step explanation:
Inattention is often not caused by relaxation or sleep but rather the result of concentrating on multiple tasks. Our ability to focus is limited and when divided, it can result in inattention. Studies like the one by Daniel Simons and Christopher Chabris demonstrate inattentional blindness, where people engaged in a complex task like counting passes among basketball players failed to notice a person in a gorilla costume on the screen. This is a classic example of our attention being so absorbed by one task that we miss other unusual or unexpected elements in our environment.
Our brains also prefer cognitive shortcuts known as heuristics, which make processing easier but can contribute to inattention when multitasking. In situations where cognitive demand is high, such as learning or processing new information, attentional resources are focused and can't be easily redistributed to other stimuli or tasks. This can be attributed to the energy and attention costs of conscious thought.