Paul Heckingbottom rued missed chances at a crucial stage of the game as his Barnsley side lost 1-0 to QPR at Loftus Road.
Josh Scowen's long-range strike against his former club gave Rangers victory in a match where they played the final 19 minutes with 10 men after Ryan Manning was sent off.
Barnsley head coach Heckingbottom admitted his relegation-threatened team paid the price for failing to score during a first-half spell in which their opponents looked vulnerable at the back.
"When we were on top we couldn't capitalise and that's what costs you. That's been our season," he said.
"QPR had a spell in the second half where they got some momentum and I thought that was the only spell in the game where they won the duels.
"They managed to score in their spell and we didn't in ours.
"Sometimes it's hard against 10 men. You saw that most of our chances came in the first half when we found space.
"In the last 20 minutes, when they had 10 men, they killed the space and it was difficult and credit to QPR as they defended well.
"That's what this league is. It's a harsh league and we're where we are because that game was a reflection of our season - we've been on top and created chances and not taken them.
"In most games we've given minimal chances away but there are ruthless players who can kill you."
Rangers boss Ian Holloway said: "It was a huge performance and result, especially as we didn't play that well.
"We ground it out. You don't always flow. This is a learning thing for us.
"How we didn't score a couple more I don't know, but I felt totally exhilarated with the pace of our breaks late on."