This rule of Scrum aligns with the Agile Manifesto principle “The most efficient and effective method of conveying information to and within a development team is face-to-face conversation.”  In-person attendance of all Scrum Team members allows for the plan to unfold with minimal communication overhead and for the team to keep the meeting within the short time-box.  In-person attendance also allows the team to effectively collaborate in the work of creating the plan. The efficiency and effectiveness of the Product Owner’s presentation of the Product Backlog is optimized as well as the Development Team’s ability to collaboratively assess and select what it can and will accomplish in the Sprint. It also allows for everyone to be clear about the Sprint Goal and why the Development Team is building the increment. In-person attendance also allows the Development team to efficiently and effectively come to a decision as to how it will build the increment of functionality. In-person participation of all team members also increases the likelihood that the team will create the right design for the increment.  If even one team member attempts to attend this meeting by any other means, either by phone or even video conferencing, efficiency and effectiveness of the planning becomes compromised. Compromised collaborative planning yields compromised collective ownership. The successful delivery of the Sprint Goal requires full commitment on the part of the whole team. Lack of in-person participation increases the likelihood that the team will fail to deliver on its Goal because the planning will lack effectiveness. People are prone to estrangement from hazy goals reached through ineffective planning. In-person planning, therefore, is paramount to succeeding with Scrum.