Wundt's approach ultimately failed because of the lack of reliability of his methods.
A scientific approach tests assumptions about behaviour
reliance on objective and systematic methods of observation, knowledge acquired using the scientific method is more than just passive acceptance of theories about behaviour.
establish the causes of behaviour through the use of methods that are both empirical and replicable
Instrospection is not particularly accurate
Nisbett and Wilson claim that we have very little knowledge of the causes of and processes underlying, our behaviour and attitudes.