Have your work cut out
Definition 1 of 2
Pro Tip 1/3Task Magnitude
The phrase suggests a task is so large or challenging that full effort is necessary. 
Finishing the marathon with no training, he had his work cut out.
Pro Tip 2/3Time Pressure
Often implies a tight deadline making the task even harder. 
With the essay due tomorrow, Jane had her work cut out.
Pro Tip 3/3Undertone of Doubt
May imply a doubt that the task can be completed successfully. 
He has his work cut out repairing that old car by himself.