Philipp Krehl has a very thorough, practical article up on Mind the Product called Product Discovery or Product Delivery: How do you Decide? His main thesis is that figuring out when it’s safe to move to the build/delivery phase of a project is all about your level of certainty about the problem you’re solving. He proposes a simple rubric to calculate your comfort level with different product risks:
If you and your team have marked every answer a 3 or below, it confirms that you have a high degree of certainty about your path, and you can start building. You will probably still discover new information but you can just adapt to it — this is why we work with Agile methodologies like scrum or Kanban.
Answers marked with 4 or above indicate areas where you should invest and do product discovery to reduce your uncertainty. At this stage, it’s better to figure out the right thing to do rather than commit to an outcome.
Once you have identified areas which require more understanding you can use an effective technique called Assumption Mapping.
He also provides a good overview of the value and practical aspects of Assumption Mapping, a method I am keen to try out.