Marketers don't stay within the limits of sanity, and they always overdose on pessimism and optimism. They have to. The only way to know we've exhausted all potential opportunity from markets—the only way to identify the top—is to push them not only past the point where the numbers stop making sense, but beyond the stories people believe about those numbers.

What do I think is true but is actually just good marketing? Am I prepared to handle risks I can't even envision? Which of my current views would change if my incentives were different? What are we ignoring today that will seem shockingly obvious in the future? How much have things outside my control contributed to things I take credit for? What's always been true? What's the same as ever?

The typical attempt to clear up an uncertain future is to gaze further and squint harder—to forecast with more precision, more data, and more intelligence. Far more effective is to do the opposite: Look backward, and be broad. Rather than attempting to figure out little ways the future might change, study the big things the past has never avoided.

The night before the D-Day invasion, Franklin Roosevelt asked his wife, Eleanor, how she felt about not knowing what would happen next. "To be nearly sixty and still rebel at uncertainty is ridiculous isn't it?" she said. It is. But we do. We always have. We always will. The idea that what lies in front of us is a dark hole of uncertainty can be so intimidating, it's easier to believe the opposite—that we can see the future, and that its path is logical and predictable. No belief in history is as commonly held, and no belief is as consistently wrong.

People will disagree, even as access to information explodes. They may disagree more than ever because, as Benedict Evans says, "The more the Internet exposes people to new points of view, the angrier people get that different views exist." Disagreement has less to do with what people know and more to do with what they've experienced. And since experiences will always be different, disagreement will be constant. Same as it's ever been. Same as it will always be. Same as it ever was.