"Differentiated instruction is provided with facilitated interactions at the point a student needs support to stay on their 'learning edge' of the zone of proximal development. This sensitive alert system within situational environments offers just-in-time interventions and differentiated educator roles to support individual student needs."

This is a quote from an article (p. 23): Patrick, S., Kennedy, K., & Powell, A. (2013). Mean What You Say: Defining and Integrating Personalized, Blended and Competency Education. International Association for K-12 Online Learning.

The statement struck me in that it explained so concisely why we need personalized learning. Also, the terms used fell in my interest: differentiated instruction, facilitated interaction, learning edge of the zone of proximal development (ZPD), alert system, just-in-time interventions, and individual student needs. Specifically, I think the "learning edge of zone of proximal devevlopment" is the key reason for why we are doing personalized learning. To accurately detect the learning edge of ZPD of each individual, dynamically and at scale, would need tremendous and delicate efforts. It can be done by human teachers, but the workload would be too much for them. So, we here need technologies to help, such as learning analytics. Once the ZPD is identified by the technologies, teachers can use the results to provide differentiated instruction accordingly. 

However, the ZPD detecting is mainly from cognitive aspect for technology to help. I suppose, other information from affective, meta-cognitive, and humanist aspects would also need technology to help obtain.