Some ideas endure for eons. They pass into legend.

Our work is often less enduring than Atlas’. Yet, we are wise to ask about longevity — for how long do we expect our idea to shine, to hold up some portion of the sky, to remain a fixture in the imagination of our audience (especially in this age)?

An automobile designer once told me to look at any vehicle considered to be a "totally new" design. This new idea was likely conceived in clay at least three to six years before. And as an idea, it ought to endure for at least another three hence. In other words, those automotive ideas — architectural, mechanical — come into the world and are expected to hold our attentions for at least a decade. The same measure could be applied to many books, to buildings, perhaps clothing, even software.

How long do we need this idea to thrive?

In answering, we learn much about how to judge what works. We learn even more about the forces which surround any idea: its dependencies, its sustaining costs, its place in the grand scheme of other ideas.

We also learn what we can never know (often, "is it guaranteed to work?"). We learn that ideas are risk, and if we want to endure we must first put ideas out into the world.