Baggies debutant Peter Odemwingie grabbed the only goal of the game.
After seeing the Black Cats lose to Premier League new boys West Brom, boss Bruce said: "In the first half we simply weren't good enough. We were 10 yards off it and unfortunately it has happened too many times away from home.
"We were a different team from the one that took Birmingham on last week (at the Stadium of Light) and unless that changes, and we take part in the game better than we did, then our dismal away record is going to keep like that.
"We have to improve, and we did in the second half. But it shouldn't take me ranting and raving at half-time.
"Mentality is what it is, and we have to try to change that if we are going to improve and take the club forward."