Sisyphus was a figure in Greek mythology who was condemned for all eternity to repeat the task of rolling a huge boulder up a mountain. Once it neared the top, it would escape him and roll down, and he would have to begin again.

So, "Sisyphean task" or "Sisyphean journey" has come to mean an insurmountable or nearly insurmountable task, journey or endeavor... which many Producers & Directors feel when taking on a full-length feature or documentary!