Individual errors led to both of Marc Janko's goals for the Sky Blues at AAMI Park, where the hosts pulled one back late on but couldn't square things up against Graham Arnold's side, despite the visitors finishing the game with 10 men.
In their previous outing City gave up a 2-0 lead to draw 2-2 at home to the Central Coast Mariners, with their latest sloppy result prompting some soul-searching from their Dutch coach.
"In the end you can say maybe it's quality," he said.
"That's something we have to analyse. But that's not what I believe. I think it's believing more strongly in what we can do.
"The belief is sometimes not there. Having a bit of fear. With fear you're never going to win games."
Asked what City need to do to start performing more consistently, he said: "We turn it around by winning."
"We're not far off. We make it ourselves very difficult. We're in a phase where we're making mistakes and getting punished. The opponent makes mistakes and we don't punish them.
"They got us a present from us."
"There's things we have to look at this week and see how we can change things around ... or by getting one or two, or three or four players in. But I'm not going to say we're going to do that."
As for the time scale of City's potential improvement, van 't Schip knows the clock is ticking as far as supporters and his employers are concerned.
"We cannot wait forever," he said.
"In the end it has to change quickly. Or it will have consequences for the club. We have to step up.
"We have to stick to what we know and believe because that's the only way. Otherwise, if we start changing and doing things I don't believe in, then I don't think I'm in the right position. I'll continue doing what I think we should do and I believe in."