The phenomenon of countertransference () was first defined publicly by Sigmund Freud in 1910 ("The Future Prospects of Psycho-Analytic Therapy") as being "a result of the patient's influence on physician's unconscious feelings"; although Freud had been aware of it privately for some time, writing to Carl Jung for example in 1909 of the need "to dominate 'counter-transference', which is after all a permanent problem for us". Freud stated that since an analyst is a human himself he can easily let his emotions into the client. Because Freud saw the countertransference as a purely personal problem for the analyst, he rarely referred to it publicly, and did so almost invariably in terms of a "warning against any countertransference lying in wait" for the analyst, who "must recognize this countertransference in himself and master it". However, analysis of Freud's letters shows that he was intrigued by countertransference and did not see it as purely a problem.