In 1964 when S. Chapman and I concluded that there is some ''unknown'' quantity in the solar wind controlling the development of the main phase of geomagnetic storms. This statement was based on our study of the variety of the development of geomagnetic storms and on the resulting conclusion that the Chapman-Ferraro's solar wind flows around the Earth and confines the Earth in a cavity (the magnetosphere) but does not transfer the energy to the magnetosphere. It was thought to be an outrageous statement, since it had been firmly believed in the 1960s that a strong solar wind was all that was needed to cause geomagnetic storms. Our search for the unknown quantity in the solar wind eventually led us to a study of auroral/magnetospheric substorms, which, in turn, led us to the conclusion that the unknown quantity is the north-south component of the IMF, or more accurately, a specific combination of three parameters: the solar wind speed V, the IMF magnitude B, and its polar angle &thgr;. This paper describes a personal account of the history of this search for the unknown quantity. One important lesson I learned during this research is that a scientific field is often in trouble when the majority of researchers agree on one particular theory or one particular interpretation of observations. In general, one particular theory in a scientific field, however popular it may be, is eventually bound to fail. Thus, when the majority of researchers believe in that particular theory for a very long time, it means that the advance in that field is temporarily stalled. ¿ American Geophysical Union 1996