Attentional Blindness
By concentrating on one aspect of life we generally have to give up paying attention to other things. We usually have a choice - we can focus on one thing and miss the rest or we can generalize, pay attention to the big picture and lose the detail. Concentration is inversely proportional to total awareness.
Being aware of having to pay attention is stressful. Sharing the burden is both efficient and safe.
Working as a crew it is possible to have the best of both worlds. Each crewmember is responsible for a specific aspect of the task and is also trusted to maintain an overall focus of the operation.
For example, X is flying and Y is looking at insect damage of the forest. Upon seeing another aircraft in the area coming from X's blind spot, Y lets X know its position. Simple.
A well functioning crew works on the byline "If you see something, say it."
In Search of the Perfect Crew