A popular saying among American GIs during the war was "we own the day, Charlie owns the night". How was the life as an infantryman, from O'Brien's perspective, different during the day than it was the night?

During the day, the soldiers would run patrols, at night they'd be mortared or killed where they slept in their fox holes. The American soldiers were bogged down by noisy equipment, and the Viet Cong moved stealthily through territoy they were acquainted with. Daytime gave the men some semblance of protections, during the night they were sitting targets.