The Bulldogs whittled a 57-point deficit down to five points during a frantic second-half rally before losing by seven.
But McCartney was in no mood to talk about the positives.
He said his side had been taught a lesson in the first half.
"We got a nice reminder that when we don’t want to do the basics of the game and work hard and make it tough for the opposition to move the ball, it's a pretty difficult game to play," McCartney said.
"To their (Lions') credit they were hungrier than us in the first half, they were harder around the contest than us in the first half and they worked harder.
"We know the journey we're on, we just got a nice reminder tonight as a footy club how hard this business is and how much work's in front of us."
McCartney said the Bulldogs were 25 to 30 per cent along that journey of team development.
He was full of praise for third-year midfielder Tom Liberatore who continued a stellar season with 27 disposals and a staggering 14 clearances to lead a revival alongside Luke Dahlhaus, Ryan Griffen and Will Minson.
After winning four of their past seven matches, McCartney refused to use the excuse of being flat.
"When we move away from the things that are distinctive to us, we get into real trouble," he said.
"They're nothing outlandish, they're just the basics of the game. It's a strong contest and it's making early defensive decisions and playing the game as it unfolds, and we got back to that and got a better result."
Griffen (ankle) and Robert Murphy (head) were cleared of injury.
