In 1972 researchers Fergus Craik and Robert Lockhardt developed a model for information processing in the brain. They proposed that memory is dependent on the depth of mental processing that was expended in the processing of that memory.
Furthermore, the depth of processing predicts how long the memory trace will remain. Depth refers to the attention, focus, elaboration, and emphasis on a particular memory. For example. with the business of an average person's day we are constantly bombarded with information (casual conversation, instructions, news, etc) but very little of this information is processed very deeply and therefore is recalled only in very general (or even vague) form. However, important information (relationships, salient work details, emotional events, etc.) require deeper processing which leads to more specific and detailed memories.