Mental set is the tendency to approach new problems using strategies that have worked in the past, even when those strategies are no longer optimal. While relying on proven strategies is often efficient, mental set becomes a barrier when a problem requires a novel approach. Abraham Luchins (1942) provided the classic demonstration: after participants practiced solving water jug problems using a complex three-jug formula, they continued applying this formula to subsequent problems that could be solved with a much simpler two-jug method.
Luchins' Water Jug Experiments
Participants were given jugs of specified capacities and asked to measure an exact amount of water. The first several problems all required the same complex formula: B - A - 2C. Critical test problems could be solved either by this complex method or by a much simpler approach (A - C or A + C). Participants who had practiced the complex method overwhelmingly used it on the test problems, while control participants (who had not practiced the complex method) easily found the simpler solution. This mechanization of thought demonstrates how successful experience can paradoxically impair flexible thinking.
Luchins found that simply instructing participants to "Don't be blind!" before the test problems significantly reduced the mental set effect. Taking breaks, changing the problem context, working with diverse collaborators, and explicitly generating alternative approaches can all help break mental set. In organizational settings, techniques like brainstorming, design thinking, and red-teaming are designed to overcome the collective mental sets that develop within groups.