Most Sprint Planning advice focuses on mechanics: how to estimate, how to size the sprint, how long the meeting should run. The more consequential mistakes tend to be less visible than mechanics, and teams that get the mechanics right can still plan badly.
Planning the "what" without genuinely agreeing on the "why"
A Sprint Backlog full of well-estimated, well-understood items can still represent a bad plan if the team never arrived at genuine, shared conviction about why this particular set of items, in this particular order, is the right one. The Sprint Goal exists specifically to prevent this: it's supposed to be the answer to "why does this sprint matter" that the whole team actually believes, not a formality generated after the item list is already settled. Teams that write the Sprint Goal last, as a summary of what they've already selected, get the sequence backward. The goal should shape the selection, not describe it after the fact.
Treating capacity as a number instead of a conversation
"How much can we commit to?" easily degrades into a numbers exercise (last sprint's velocity, this sprint's available hours) when it should be a conversation about what's actually realistic given specific, current circumstances: who's on leave, what unplanned work historically shows up mid-sprint, whether the team is carrying unfinished work from last time that will eat into capacity before new work even starts. A velocity number smooths over exactly the situational detail that determines whether a specific sprint's commitment is realistic.
Under-planning the "how," and discovering the gaps mid-sprint
Sprint Planning's third topic (how the selected work will actually get done) is the one most likely to be rushed once the "what" and "why" are settled and everyone's ready to end the meeting. Skipping a genuine conversation about approach means technical disagreements, missing dependencies, and unclear task breakdowns get discovered during the sprint instead of during planning, when they're far more expensive to resolve. A brief but real discussion of approach for at least the more complex or uncertain items in the sprint catches a meaningful fraction of these problems before they cost anything.
What actually distinguishes good Sprint Planning
The best Sprint Plannings share one trait more than any specific technique: the team leaves genuinely believing in the plan, not just having produced one. A plan that technically satisfies the format (a Sprint Goal exists, items are selected, capacity is accounted for) can still be a plan nobody in the room actually trusts. That gap between a technically complete plan and a genuinely believed one is where most Sprint Planning failures live, and it's not fixed by better mechanics. It's fixed by treating the "why" and the "how" with the same seriousness as the "what."