Liverpool twice surrendered a two-goal advantage and conceded a stoppage-time goal to go down 4-3 at Bournemouth last Sunday.
“This game helped us to understand what's wrong with our protection sometimes,” Klopp told a news conference.
“We played good enough to win the game until it slipped through our fingers. We were passive, which is not usual for us.
“At 3-1 up we played one bad pass and they scored. They used that situation. It was our fault. We were responsible for it.”
Klopp said he was surprised by West Ham's lowly position of 17th in the table.
“We will be angry (on Sunday). But West Ham will be a tough challenger, an interesting game,” the German added.
“Nobody would have expected West Ham's situation in the table. They have had injuries. They all come back to play us but that's not a problem.
“West Ham want the points and that makes me angry just thinking about it.”
Klopp confirmed that Liverpool's Cameroonian centre back Joel Matip would not represent his country at the African Nations Cup in January and ruled striker Daniel Sturridge out of the West Ham match.
Sturridge picked up a calf injury in training that kept him out of the trip to Bournemouth and Klopp said he had no idea when his injury-prone forward would return to training.
“Until now he hasn't trained,” the manager said. “He's not with the team. He's not happy. That's the life of footballer. You can't force these things.”
Original source: Klopp backs ’angry’ Liverpool to beat West Ham