Garry Monk's side conceded two late, quickfire goals to slump to a 2-1 loss and slip out of the Championship play-off positions.
Winger Harris told The Star: "Everyone is very disappointed, including myself.
"We were a few minutes away from winning the game, and ended up losing. We just have to take it on the chin.
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"We have to have a reaction and not let it happen for the rest of the season.
"If you want to get promoted you can’t let leads slip like that in the last few minutes, and end up with no points."
Tosin Adarabioyo's looping header and John Buckley's deflected strike ensured the Owls left Ewood Park empty-handed. Defeat leaves them in seventh position, four points off leaders Leeds United.
On their late collapse, Harris said: "I wouldn’t put it down to anything in particular. Maybe a lack of concentration because I think the boys have done brilliantly.
"We stuck to the gameplan from the first minute and it was all going well until five minutes before the end.
"We have thrown it away, but we have to learn from this and make sure it doesn’t happen again.
“It’s important we learn lessons if we want to get promoted. It’s a long season ahead of us.
"I thought everyone was excellent, it’s a difficult place to come.
"It’s a disappointing end to a good performance."