Scott McDowell, for The 99 Percent:

Current neuroscience research confirms what creatives intuitively know about being innovative: that it usually happens in the shower. After focusing intently on a project or problem, the brain needs to fully disengage and relax in order for a “Eureka!” moment to arise. It’s often the mundane activities like taking a shower, driving, or taking a walk that lure great ideas to the surface.