His claim is that doing a ton of really hard work repeatedly is still a lot faster and more reliable than waiting under the apple tree for a flash of inspiration.

The flash-of-inspiration mode of creativity has been dramatized so much that most of the population assumes that's just how it's done. It also seems way easier than hard work, so people want it to be true when they try to be creative. Simultaneously, it seems way less attainable than plain old hard work (the requirements seem to be mostly circumstance), so people also want it to be true when they are not trying to be creative ("My great idea just hasn't come to me yet!").

JC is reminding us of the hard truth: the reality behind the stories is that creativity is the prize of determination, not serendipity.