The history of computer interface shows us a different perspective about usability: Usability means not "easy to use", but "thinking to use". To make this clear, this paper first focuses on two important persons involved in developing the computer interface; Douglas Engelbart and Alan Kay. Next, the Star information system, announced by Xerox, is considered in order to explore why the paradigm discussed in this paper occurred. Engelbart was influenced by B.L.Whorf and explored the relationship between body sense and language. To investigate this relationship, he sought to connect "action" and "looking" via the computer screen. Therefore, Engelbart and his group invented the mouse as a pointing device that translates "action" into images on the computer screen for "looking". In this "action" - image - "looking" circular process, Engelbart wanted to allow new ways of thinking by using a computer. On the other hand, Alan Kay coined the slogan, "Doing with images makes symbols" to develop a different computer interface from Engelbart. Kay were affected by J. Bruner and focused on the link between "image" and "looking" as a thinking process. His overlapping window system was invented to fulfill Kay's intention. He wanted to make a strong relationship between "image" and "looking" in order to build a fantasy on the computer screen via controlling images. This requires the user to construct his/her own way of visual thinking way. Engelbart and Kay didn't intend to develop "easy to use" interfaces but "thinking to use" interfaces, capable of amplifying the human intellect. However, the basic elements that they invented for the computer interface contribute to developing "easy to use" interfaces and gave birth to the Star workstation. The concept of Star changed the meaning of usability to 'easy to use without thinking'. However, we must revisit Engelbart and Kay's ideas in order to open new possibility for the human- machine symbiosis.