What was a fundamental problem with the introspectionist school of psychology?

Answer and Explanation

Introspection was Method by which trained observers carefully reflect and report on their mental experiences.

The fundamental problem with the introspectionist school of psychology was that the use of introspection as an experimental technique was often criticized because Introspection was limited in its use; complex subjects such as learning, personality, mental disorders, and development are difficult or even impossible to study with this technique and also different observers often provided significantly different responses to the exact same stimuli This was a bigger challenge to introspectionist school of psychology