Sprint planning meetings are often chaotic, with half-baked stories and lots of assumptions and clarifications left open. In such instances, the planning sessions are often hijacked and the estimates are given by the managers or architects. As a result, these sessions do not make the team self-organized, and we tend to follow Scrum-But rather than Scrum (conduct planning session -- Scrum -- but estimates are given by managers -- But).
Upon analysis, a few reasons for this could be lack of domain knowledge, a fairly new team, lack of managers' trust in the estimates of the team, and so on.
As kids, most of us have sketched a "mind map" as part of our homework activities. For example, food:
Mind map: Food groups
The teacher's intention was to make her students visualize the different food groups and represent them graphically.
Over the years, we seem to have forgotten what we learned as kids. During the sprint grooming sessions, the team could be prompted to draw a mind map of the story on the whiteboard. Example:
Mind map: Log-in functionality
Now let's look at the benefits of the mind map on stories:
A mind map can be used as a tool during the grooming session to arrive at the task-based estimates.
A mind map enables the team to visualize the requirement down to the lowest level.
The different actors and activities can be identified and designed.
The test cases can be derived from the mind map.
Stories can be split logically, with indicators such as "must have," "could have," and "nice to have."
The mind map helps identify dependencies and prompt the team to ask for clarifications.