'Believe your indications' as part of conservative decision making and safety culture

'Believe Your Indications' has been a well-known principle of nuclear power plant operational safety from the very beginning. It is the foundation of conservative decision making and is a vital component of a strong safety culture. Unfortunately, this principle is apparently not uniformly honored. 'Believe Your Indications' is also strongly related to the avoidance of 'rosy assumptions'. Multiple actual examples indicate widespread applicability. Executive action to support incorporating this idea into the safety culture is indicated. (author)