Why was trench walfare often a difficult method of fighting

It was difficult because of the conditions and the little time the soldiers had to dig these massive trenches. Also because the enemy would often build their trench less than a hundred yards away. When the enemy got pushed back they would often turn around the enemies tench and use their trench so they didn’t have to build a new one.

Cbecause it’s c and this needs to be 20 characters long