Conditional probability arises as a tool for analyzing a strategy for decision-making that molds to new conditions. From that point of view, an introductory sequence which utilizes diachronic games is designed and analyzed under the framework of didactical engineering, bringing conditional probability into play as a decision-making tool. It can be observed that students tend to base their decisions on heuristics and experiential considerations, and do not see the need for a proper calculation of theoretical probabilities. At most, they use experimentation as a tool, not computing probabilities based on relative frequencies, but comparing absolute frequencies.