On-loan Chelsea forward Tammy Abraham scored a brace to condemn the Terriers to a sixth Premier League game without a win.
Despite admitting that Huddersfield should have been braver, Wagner believes that the outcome may have been different had a number of key situations gone their way.
"The penalty decision was 50-50 and there were a lot of unlucky situations," the German told reporters after the game.
"In the first half [we were] not good enough, not brave enough - I think bravery was a big problem for us today.
"I think we created moments, we hit the bar and had a number of dangerous situations in the six-yard box, but unfortunately we were not able to score.
"But this is exactly the situations that I meant - you have to invest in bravery if you like to be lucky."
Huddersfield currently sit 11th in the Premier League table with nine points from eight games.