c2263325_culty_Institute___What_is_PBL___WHY_
[WHAT:] Creates cognitive conflict [HOW?] Select cases with information that makes simple solutions difficult: while the solution may address one part of a problem, it may create another problem. Challenges prior learning as noted above. [WHY?] 
The literature suggests that learning takes place when there is a conflict between prior learning and new information.
Problem-Based Learning Faculty Institute - What is PBL?
WHY?