It’s pretty simple. Most projects fail to meet estimates, and the reason we are estimating is so we can determine:

• do we possess the resources to complete a project?

• can we finish on time?

• is the project even worth it?

But when a project is unlike anything the team has accomplished together, the early estimation will be a overly optimistic wild guess. What’s more, if a rigid cross-team timeline is built on our fictional estimates then we'll end up too far behind to allow for mid-course corrections.

So the solution is to measure all the "risk" upfront through lean experimentation. And by "risk" I mean the unknown bits that defy accurate estimation.

So, identify the unknowns, slice them into thin experiments, dedicate resources, time-box each experiment, and complete only enough until it is "knowable" then scale estimates accordingly.