Ignoring the role of soil suction and implementing unsaturated soil mechanics when assessing slope stability in Indonesia is a common practice. One of the main reasons is due to the precognition that incorporating soil suction means using higher shear strength, which leads to less conservative analysis, while it is difficult to practically obtain accurate input parameters for unsaturated soil analysis. However, a number of slope failures occur all over the world due to rainfall, which becomes evidence that ignoring the role of soil suction may not necessarily lead to a conservative result. On 9 January 2021, rainfall-induced slope failure occurred at Cimanggung after four hours of heavy rainfall and killed 32 people. Many of them were injured, and houses were destroyed. This event shows the significance of considering the interaction between infiltration and soil suction when conducting slope stability analysis. Difficulties in obtaining input parameters for unsaturated soil analysis experimentally hindered practitioners in applying unsaturated soil mechanics. While the parameters can be estimated, it is always of question whether the estimated parameters are sufficiently accurate for practical purposes. In this paper, conventional site investigations were carried out while unsaturated soil parameters were estimated to study the mechanism which triggers the landslide that occurred at Cimanggung. It will be shown that estimating unsaturated soil parameters can be practically accurate and manage to capture the failure mechanism such as critical rainfall duration and critical slip surface.