Just because we set an objective doesn’t mean we’ll reach it. At least not in the specific form we imagine.

When we do finally reach a destination that’s descriptively similar to the objective we thought we were after (artificial intelligence, augmented reality, flight, fusion, et al), it will look wildly different in practice than we thought.

Once we achieve a breakthrough innovation, along the path of stepping stones — the series of building blocks we must pass through to get us there — we’ve made hundreds of additional observations on the journey that change what...