When you're producing something that's above the norm, not easy, even risky, you might end up hitting a small glitch while preparing your idea for the 'big' meeting. It happens, don't freak out.
On the flip side, when you hit that bump while you're producing the norm, the standard, the I've seen those before' kind of work—it's a whole other ball game. The bump comes unexpectedly. It's surprising. It raises questions.
Both bumps require you to push off a deliverable for a day or so, but only one of them will be viewed more acceptable to your client.