no matter how intensely we desire certainty, we should understand that whether because of our limits or randomness or future unknowable confluences of events, something will inevitably come, unbidden, through that door. Some of it will be uplifting and inspiring, and some of it will be disastrous. We all know people who eagerly face the unknown; they engage with the seemingly intractable problems of science, engineering, and society; they embrace the complexities of visual or written expression; they are invigorated by uncertainty. That's because they believe that, through questioning, they can do more than merely look through the door. They can venture across its threshold. There are others who venture into the unknown with surprising success but with little understanding of what they have done. Believing in their cleverness, they revel in their brilliance, telling others about the importance of taking risks. But having stumbled into greatness once, they are not eager for another trip into the unknown. That's because success makes them warier than ever of failure, so they retreat, content to repeat what they have done before. They stay on the side of the known.