Context is king
I know the common phrase is “content is king”, but as far as Agile is concerned it’s context that is key.
When a team starts a new initiative, it’s important that they understand who it is for, why it is important, what value is it expected to provide, what problem(s) will it solve, etc. Without this context, the team can’t be expected to know if they are building the right thing — all they can do is follow the Product Owner’s direction.
As much as we look to the PO to represent the stakeholders’ needs, the development team need to understand the bigger picture: how does this feature fit into the product? With a wider context, the team can think about a general technical direction, bearing in mind things will change and the project might end before finishing the whole thing (hopefully because the customers are happy rather than running out of time/money).
The team can also identify risks, dependencies and unknowns — not all of them, of course, because there will always be discoveries as they dig deeper. They can create spikes, run experiments, build a proof of concept, and/or change the prioritisation of the backlog in order to reduce those concerns. This is a big difference from my experience of waterfall projects where the project manager would fill in the risk assessment sheet and file it away.