Final answer:
The Luchin's Jar Problem illustrated the concept of mental sets, where individuals persist in using a strategy that worked in the past, even if it's not effective for the current problem.
Step-by-step explanation:
The Luchin's Jar Problem illustrated mental sets. A mental set occurs when individuals persist in approaching a problem using a strategy that has worked in the past, even if it's not effective for the current problem. In the case of Luchin's Jar Problem, the subjects had a fixed strategy that they used for all previous tasks, and they failed to adapt when a new strategy was required for a set of new problems.