Question

Why was it difficult to gain an advantage over the enemy in trench warfare?

Answer 1

You were in the ground, so basically once you were basically in a bad positions (during certain problems).If the enemy knows your there, they could throw a grenade... Everyone gets out and starts running... This basically gives the enemy and advantage to start shooting back at you. If you could dig fast enough (hard to do) you could have dug under them and come from behind them and kill them.