Let’s compare Instagram and SpaceX. Arguably both are extremely successful companies but Instagram is an unpredictably successful idea while SpaceX was a predictably successful.
When Instagram started, there were tons of photo-sharing apps and the thing that would cause one to dominate all the others was totally unknown - there was no way to say “if the instagram team can figure out X, Y, Z then they will win.” (Beyond the obvious ‘if they can get lots of people to use their service’ - X, Y, Z need to be some sort of clear intermediate success factors - leading metrics.)
When SpaceX started, they could say “it will be frakking hard but if we can get profitable launch price below $100/kg, we will win.” (June 2020 costs are $2700/kg and the fully-reusable starship will supposedly get costs below $10/kg.) You can add up all the factors contributing to launch cost and systematically work on bringing them down. These are the known unknowns that a team can execute against.
Executing might have a high chance of failure - it might just be too expensive, take too long, be physically impossible, killed by regulation or danger or one of a million other things.
The description of the inability to find leading metrics for an unpredictably successful idea sounds like The Map is not the Territory and why §Program Design - effectively the ability to describe the territory well with a map - is coupled to predictably successful ideas. To go one step further, because Technological roadmapping can give an idea of where technological evolution can go and how to get there you could argue that roadmapping is a way to turn ideas into predictably successful ideas.
Another way to think about it: predictably successful ideas are risky but not uncertain. Or at least they constrain uncertainty. Uncertainty always involves risk but risk does not always involve uncertainty.