The purpose of this article is to describe the process of a proof construction. It is more specific on the failure of the process. Piaget's frameworks, assimilation and accommodation, were used to analyze it. Method of this research was qualitative method. Data were collected by asking five students working on problems of proof using think aloud strategy. Students' works were compared with the problem structures. Based on the data analysis, it shows that there were three causes of failure of proof construction. The failure occurs on constructing proof because (1) Incomplete schemes on assimilation, (2) Incomplete schemes on accommodation process, (3) Complete schemes but unrelated on assimilation and accommodation process.