Information observed during construction can be used to optimise the rest of the construction or structure. In this article nine general conditions are named for the implementation of the Observational Method in geotechnical engineering. The most important general condition is that the uncertain field condition (the observational data) must be clear to measure. The problem of brittle behaviour is related to this point. If a project fulfils all general conditions, a financial risk analysis is necessary to find out if the Observational Method is profitable. In this article a simplified approach for a risk analysis is given, inclusive two examples, which show that the success of implementation varies strongly per geotechnical discipline.