After working on a calculus problem for three hours, Sue took a two-hour break before going back to the problem. She solved the problem soon after she returned to it. Wallas would refer to Sue's two-hour break as a step to problem solving called .

Incubation

Explanation:

Incubation is the stage of creativity.  

These stages are :

Incubation is the second stage of creativity. It is a combination of unconscious thoughts. These thoughts are stimulated by the conscious work of mind at a spot of time. Incubation is related to insight and intuition. This a validated process. The process to leave a problem for a short period and after that, the solution accidentally pops up. This is the result of the incubation.

answer; people have no objective standard by which to judge themselves;