Operator Over-Confidence
At Chernobyl-4 (the reactor used in the test), the surrounding influence did not tend to promote the operators to carry out a cautious test. The plant was set up as a model of all the RBMK type plants where reactors were cooled by water and moderated by graphite. This was considered to be worthy of copying and to be the best.

As a result, "Its operators felt they were an elite crew and they had become overconfident."

Also, the evaluation was realized as an electrical test only and it is thought that the test was under the supervision of the turbine manufacturer and not the regular operators.

As a result, "The operators did not think carefully enough about the effects on the reactor." 

Furthermore, if the test was not completed with satisfaction at this time (April 25, 1986), the people would have to be delayed another year for the next shutdown as the test was scheduled to be done just ahead of a planned reactor shutdown for regular maintenance.

As a result, "The operators felt under pressure to complete the test this time." 

The operator room.