Freo had few four-quarter performers on the day, with 10 players registering 13 possessions or fewer as the Roos consigned the visitors to their sixth loss of the season.
"With some of our players the difference between their good and their bad is still too much at the moment," Harvey said.
"I've got to make them realise that and understand the missing link in between, otherwise we rely on too few to try and win these games.
"Once again there was evidence of that today."
Fremantle looked set to continue a spirited month of football that has seen the club recover from an 0-4 start to the season when it led by 26 points at quarter time. But it was a different side that came out after the first break.
"It was a good start, but we need to be able to sustain that on the road, particularly," Harvey said.
"[We need to] get right on top of oppositions and don't give them any hope of thinking they're a chance in the game.
"They started winning the contested ball [after the first quarter].
"I did manage to hear Dean [Laidley] let go at his players at quarter time, so I made our players aware of it. They knew what was coming."
Harvey also bemoaned his onballers' inability to take advantage of the lopsided hit-out count – 52 to 15 – that was driven by 43 taps from giant ruckman Aaron Sandilands.
The visitors were on the wrong side of the free kick count, however, with 19 kicks awarded North Melbourne's way to Freo's nine.
Harvey tried to be diplomatic when questioned on the imbalance.
"I've got a headache … look I've spoken to [umpires boss] Jeff Gieschen on a number of occasions about, in particular, [being] on the road and what happens and we're working through that," he said.
"I don't want to use that as an excuse, and I can't, for losing, but nine free kicks doesn't represent a lot of the hard work that we did. That's all I'd say and that's happened twice in the last three weeks.
"It's what creates enormous debate in our game, but we've got to be able to have the ability to override that as a group."
Roger Hayden limped off with a calf strain midway through the third quarter of his 100th match, but Harvey was hopeful the injury was not too serious.
