Many junior staff officers knew exactly what front-line conditions were like. Reginald Tompson, then on the staff of 7th Division, wrote in his diary on 30 July 1916 that:
The conditions in the trenches which are in great part obliterated & non existent are indescribable. It takes 2 hours to go 300 yards in places, & they are up to their thighs in liquid mud, & unceasing rain continues, & where there are trenches they are often only 2ft deep. The battalions will be relieved tomorrow. 48 hours is the maximum they can stand. The food is drenched with rain before they can eat it.
Source:
Holmes, Richard. "Brain and Nerve." Tommy: The British Soldier on the Western Front, 1914-1918. London: HarperCollins, 2004. 240. Print.
Further Reading:
Life in the Trenches (FirstWorldWar.com)
Trench Conditions (WarMuseum.ca)
What Were the Living Conditions in Trench Warfare? (TrenchWarfareWorldWar1.Weebly.com)
You know it's bad when someone bitches about the conditions of the frontline and doesn't even mention the incoming fire.