Prepare for both success and failure

Imagine you have failed in the future.
If you acquire a new car, you can buy more collision insurance so you can replace it if you smash it. A team running a premortem analysis starts by assuming a bleak future: “Okay, it’s 12 months from now, and our project was a total fiasco. It blew up in our faces. Why did it fail?”

Imagine you have succeeded in the future.
The upper bookend requires a strategy for unexpected success. Consider a boutique designer who finds out Oprah will shortly endorse her product. Will she be ready for the surge in demand? When you bookend the future, you must plan both the best and worst outcomes. If your decision is a wild success in the future, how will you ensure that you are ready for it?

Assume that you are being overconfident.
Give yourself a healthy margin of error. Many engineers have built a “safety factor” into their projects since their computations can have life-and-death consequences. How much concrete does a dam need? How robust must an airplane wing's materials be? You can ask yourself the same way: What if my prediction isn’t as accurate as I’d think? How can I ensure customer satisfaction? What safety factor do I need?