Why should the constitution be made according to popular will?​

One of the basic principles of governance is the realization that governments exist to serve the will of the people. ... To this end, constitutions, which describe the relationship between the governed and the government, must be written with fulfilling the wishes of the governed in mind.

i believe the answer is:   psychological  experiment

in this experiment, wilhelm wundt became the first person that implement scientific method in analyzing the pyschological phenomenon.

due to this result, wilhelm wundt also able to make psychology to be acknowledged as a separate scientific field from biology.