Task Difficulty
From WikEd
Task difficulty is one of the ways that students attribute success and failure in the classroom. Task difficulty is an external locus and is uncontrollable by the student. To see more information regarding task difficulty in relation to the Attribution theory click on the link.
Reference:
Mayer, Richard E. The Promise of Educational Psychology Volume II: Teaching for Meaningful Learning. Pearson Education, Inc., New Jersey, 2002.

