Iceberg principle,

Definition of Iceberg principle:

1. Observation that in many (if not most) cases only a very small amount (the tip) of information is available or visible about a situation or phenomenon, whereas the real information or bulk of data is either unavailable or hidden. The principle gets its name from the fact that only about 1/10th of an icebergs mass is seen outside while about 9/10th of it is unseen, deep down in water.