Learning Industriousness

In an experiment, one group of students was given hard puzzles to work on and another group was carefully matched t this group, but given easy puzzles. The two groups experienced the same success rate, but ha very different expectations about the role effort played in success. Suggests that success on hard problems can be good for us, but failure is demotivating. What skills are you working on? What's your current success rate? Should you be increasing the difficulty or finding ways to reduce frustration?