At the national level, it is difficult for donors to meet the aid effectiveness principle of aligning their inputs with country priorities if a developing country has not yet established such priorities or strategies. At the institutional level, varying national circumstances or enabling environments can enhance or inhibit an intervention’s success. Site-specific environmental factors can also influence the performance of an intervention (e.g. a wind turbine will generate varying amounts of electricity depending on the prevailing wind speed). However, some interventions will lead to results that either materialise or can only be assessed after a longer time (e.g. constructing infrastructure that can withstand a l-in-100-year flood).