On Sunday, the Lions forfeited a 22-point fourth-quarter lead against Adelaide to lose by five points.
It was the latest in a string of poor fourth quarters that has dogged the club all season.
Along with Melbourne, the Lions have won just five final terms - the equal fewest in the league.
But Voss said while the Lions lost their run, it was not a lack of fitness that cost them against the Crows.
"They're fit enough, they're absolutely fit enough. All our results say they're fit enough so it's got nothing to do with that," he said.
"It's 'do you want to be able to grind it out, and can you think your way through it when the game's on the line?'
"Results haven't gone our way, so you can get a little desperate and perhaps go away from what we were doing in the first place. We've just got to keep our heads through the last quarter."
Voss said the Lions stopped spreading the ball and were looking in the corridor too often against the Crows, but said the youth of his team was no excuse.
"There's minimum expectations you have and while there's younger players out there, there's still standards you have to try and achieve and one of the expectations is you can still run," he said.
"They [the Crows] come back inside so many times.
"It's going to be hard to watch the vision and watch it over and over again. In the end they were stronger in running ... and considering it was our home ground and our conditions that was a bit disappointing."
Voss said it was not a lack of effort from his men, saying they desperately wanted to win - "you've only got to look in their eyes at the end" - but they simply were not thinking through situations well enough.
"We've been in that position plenty of times and haven't sealed the deal," he said.
"Not getting the win is very disappointing because when you've got effort and intent, you want to get some reward as a competitor, it nourishes you and we're falling a bit short of getting that."
He said defender Joel Patfull's early exit with a broken wrist had little impact on the final result.
Michael Whiting covers Brisbane Lions news for afl.com.au. Follow him on Twitter: @mike_whiting
