This paper covers the topic of data collection and how to deal with respondent’s perceptions, both in general and in relation of their life-event history in particular. This key question is central to the analysis of fuzzy states. This chapter presents the question of subjectivity, comparing facts with perception, focusing on retrospective interpretation true several example: working career, marital processes, parental universe, household head status and gender, measuring perceptions in economics, from subjective poverty to subjective well-being. These examples shoe how integrating perceptions and qualitative explorations improve and help statistical categorisation.