The majesty of a large river can sometimes overwhelm the underlying message of flow. When under control the continuous flow of water past any point is a metaphor for the flow of work through a process. The flow of work is like that of the river continuously delivering value.
Constraints that impeded the continuous can introduce significant problems requiring rework or scrap. Just ask folks in Southern Louisiana about where the Mississippi really wants to go and the benefits and problems that redirecting the Mississippi has caused. Engineer processes in a manner that provides as continuous a flow of value as possible!