A common encounter when using the Cascading framework for big data applications is the declaration of numerous data sources that merge into one or two primary transforms or operations using a complicated assembly of pipes. With this, and additional common encounter is a PlannerException complaining that a single or multiple number of these streams are not bound to their corresponding source taps, specifically:
Cascading: PlannerException not all head pipes bound to source taps. Remaining names 
Such an alert can definitely frustrate the user, and within Cascading, a multitude of scenarios can invoke this error, but the most common cause revolves around the fact that within an entanglement of numerous pipe heads streaming trough various aggregations and filters, one or more heads are not actually connected to an output tail.