Ideation is an essential process to any prospective design project. That collaborative process is cognitively demanding. Observing designers (n=133) working on prospective design projects allowed us to identify three categories of ideation problems recurrently occurring. Firstly, we identify the problems related to participants’ preparation. We notice that certain intellectual stance or lack of general knowledge is a handicap to some and impairs their ideation capability. Secondly, we introduce problems related to the focus of the ideation process. Those problems particularly affect the way the idea is developed and its scope. Finally, we discuss the idea externalisation difficulties, where we mainly deal with the language and sketching competencies required for the materialization of ideas.