Retention is the "North Star" metric for all social platforms. Understanding human psychology is the key to mastering it.
The Information Gap
Start with a question or a "mystery" that isn't solved until the end. This creates an "open loop" in the viewer's brain that they must close by watching.
Visual Pacing
Change the visual every 2-3 seconds. The human eye is designed to detect movement. Static images are "dead" to the brain.
The Micro-Payoff
Don't save all the value for the end. Give small bits of interesting information every 10 seconds to reward the viewer for staying.