Jonathan Woodgate gave his thoughts after nine-man Boro lost at Swansea.
The hosts were ahead through Andre Ayew's first half penalty, but Marcus Tavernier equalised in the second half for the Teessiders.
Ayew re-established Swansea's lead before Sam Surridge added the third for the South Wales outfit.
"When we got to 1-1, we were in the ascendancy and it only looked like one team winning the game," Woodgate said.
"I said that to the players at half-time, that it was there for them.
"It's ill discipline and that costs you. We need to learn that. When people go on the pitch we need to be able to trust them to make the right decision."
Watch the full interview with the Boro head coach in the video player above.