Although we live in an age that worships focus—we are always forcing ourselves to concentrate, chugging caffeine—this approach can inhibit the imagination. We might be focused, but we're probably focused on the wrong answer. And this is why relaxation helps: It isn't until we're soothed in the shower or distracted by the stand-up comic that we're able to turn the spotlight of attention inward, eavesdropping on all those random associations unfolding in the far reaches of the brain's right hemisphere. When we need an insight, those associations are often the source of the answer.
In a follow-up, he emphasizes the merits of boredom:
After all, when we’re bored we begin to daydream, and studies suggest that people who daydream more score higher on tests of creativity. This is why I now force myself to leave my phone behind a few times a week. When I have my phone, I check my email or twitter or the WSJ the second I get bored – the daydream is always being interrupted. So I’ve learned to embrace the possibilities of boredom.