Background: Implementing agile practices in software development processes promises to bring improvements in product quality and process productivity, but there are few reports of cases of failure to learn from. And more specifically, it is not always clear which practices work well in which contexts. Aims: In this paper we present the experience of TSol, a small Chilean-based software company where some agile practices were added to an already formalized process. They intended to prove that this addition resulted in improved performance. Method: We conducted a sequential explanatory strategy. First, an action research was applied implementing agile practices into the already existing process. Performance was measured in terms of the rate of rejected products in each process. Next, a survey was conducted by interviewing the development team members in order to know their opinion about the effectiveness of each of the applied agile practices. Finally, the obtained results were compared with scientific literature recommendations about agility implementation. Results: There were clear improvements in performance. However, there was agreement about the usefulness of certain practices while others were not or they were even felt as a barrier for appropriate project development. Some of these results are consistent with the literature while others are not. Conclusions: This work adds on the scarce lessons earned when agility implementation fails. Not counting on the few existing publications about failure cases of applying agility made TSol implement it in cases it was not recommended. Also, there are particular context circumstances that made TSol's results different from past experiences.