The term "sanity check" is used to describe an instance in which someone takes a moment to test assumptions, confirming that they are, in fact, correct. Also known as sanity tests, these checks have a number of valuable uses. Taking the time to make a sanity check is almost always a good idea, as incorrect assumptions or calculations can throw off a result, requiring additional work to figure out when the situation went wrong, and how it can be corrected. Being able to admit one's potential for mistakes is also a valuable trait to have, especially when working with others.
When someone conducts a sanity check, he or she confirms that something does indeed make sense. In the sciences, people may bounce ideas off each other to ask for such a check, reflecting the fact that an idea which sounds totally reasonable inside someone's head might turn out to be flawed after analysis by another person. This process is also used in mathematical calculations, confirming that the result of a calculation is correct by approaching the calculation in another way. For example, if someone calculated that 5 times 37 was 163, a sanity test would suggest that this answer was wrong, because multiples of five end in 5 or 0.
In the humanities, sanity checks are used to confirm that the ideas in a paper or discussion are sound and that they have a basis in provable material. A historian, for example, might ask for one from colleagues when formulating an interpretation of a series of events. Students of philosophy, sociology, and other fields in the humanities often rely on each other for checks which are designed to identify problematic assumptions and conclusions.
People may also casually ask each other for a sanity check, as in "Am I crazy, or are you driving a different car today?" Some people may describe instituting one for someone else, like "Susan thought she knew what was going on, but I gave her a sanity check and we got things straightened out." Before making a statement about which one is unsure, it is not uncommon to preface the statement with a request for a sanity test, alerting people to the fact that the statement is open to correction or clarification from someone who might know more.
The ability to ask for a sanity test is often respected by friends and colleagues, because it indicates that someone freely admits that he or she is not infallible. People may feel more comfortable making gentle corrections if a request for a sanity check is issued, while a mistake made by someone who insists that he or she is always right may go unaddressed, leading to future problems.