Informal learning usually takes place outside educational establishments, does not follow a specified curriculum and may originate accidentally, sporadically, in association with certain occasions, from changing practical requirements. It is not necessarily planned to be pedagogically conscious, systematic and according to subjects, but rather unconsciously incidental, holistically problem-related, and related to situation management and fitness for life. It is experienced directly in its "natural" function of everyday life and is often spontaneous.
Try to answer this question if possible (otherwise reply "unanswerable"):  What is necessary for informal learning?
unanswerable