It is because of this fundamental interpersonal factor that methods and techniques imposed on the teacher, efficient as they might have seemed in the abstract in terms of language-learning theory, have always proved successful for some people working with some classes but not for all. The interaction of teacher personality, multiple student personalities, and what each brings into the classroom from the outside can be observed only in unique situations. Take one student away from the group or add one student and you immediately have a new mix. Change the teacher and the situation is no longer the same. All teachers are conscious of this fact, which has been the bane of large-scale investigations and experimentation in teaching methods.
Is methodology then futile? Not at all. Methodology should be based on what we know about language (what it is and how it operates -- still a matter of controversy); what we know about human beings (how they learn and how they learn language and whether these are different processes or merely different manifestations of the same process, another question still under investigation); and what we know about people in interaction (a prolific area of psychological study). It is inevitable, then, that methodological recommendations will change as our knowledge of these three factors evolves, with earlier postulates being rejected and new premises accepted. Teachers should keep in touch with findings in these areas and share the excitement of a developing and progressing discipline.