You have your work cut out for you (idea)

Meaning: You have a great deal of work that needs to be completed.
The expression "you have a hard row to hoe" has a similar meaning.

Etymology:
"Well, looks like you’ve got your work cut out for you,” says your boss. This familiar phrase inspires dread and reinforces the obliteration of your weekend plans in a single blow. Like the series of periods at the end of an unfinished sentence, it conjures a certain sense of foreboding which surrounds the overwhelming task at hand.

Back in the days when people actually sewed garments by hand, stitching together a jacket could be a time-consuming undertaking. While the necessary pieces of cloth had to be cut out initially, this was by far the easiest part of the job and the least daunting. If someone happened to cut out these pieces of fabric for the seamstress, she might be inclined to say, “I have my work cut out for me.” In this case, the saying could be taken literally and figuratively. Metaphorically, the seamstress implies that the work ahead has been clearly laid out for her, and that she anticipates extensive labor.

So the next time your manager tells you that you have your work cut out for you, ask where the nearest sewing machine is!

This idiom dates back as far as the 1600s and appears in Charles Dickens' "A Christmas Carol".