In our worlds of instructional design, complexity is often considered to increase cognitive load. So, we training professionals try to make information as simpler as we can. Complexity can be redesigned to be offered as positive challenge to drive twice the output of simple, non-complex learning.
Psychologists have established that people retain learning better when they put effort into learning it. Learner put effort into learning when they are faced with challenging tasks. For instance, one classic study found that participants who solved difficult anagrams in their learning remembered significantly more information then participants who solved easy anagrams in their learning (Tyler, et al., 1979).
When faced with a problem-solving task, learners engage in the subject at a deeper level. Learners review the information from different angles, think about the big picture, and establish connections. Problem-solving activities have the biggest influence on training effectiveness as compared to other strategies. Effectively, challenges if built into learning actively can trigger higher engagement levels.