This study introduces an effective intuitive rule focusing on "tending to the midpoint" in individuals' mathematical thinking. The rule concerns the intuitive tendency towards choosing the midpoint of a change, as a salient point among all the points. To test the proposed rule, 120 students in grade 9 were interviewed. We analyzed the data using premises from the dual-process theory. Our findings revealed that "tending to the midpoint" is conceivable as an intuitive rule in individuals' mathematical thinking, and that the answers given to the relevant questions were much affected by the rule consisting of a salient variable as midpoint.