This is a good one. Management and understanding of state vs. just shipping all the state.
What's the top 2 examples you'd share if you had a persons attention for 60 seconds?
Composing/merging multiple packages rather than layering them saves time and makes things consistent between "containers". Systemd service description contains 90% of what you may want from docker anyway. (filesystem isolation, security restrictions, networking, lifecycle management, multiple service instances)