The level-of-processing effect (as described by Fergus I.M. Craik and Robert S. Lockhart in 1972) is a function of the depth of concentration that is applied to mental tasks. It posits that the depth of memory is congruent to the depth of thought and concentration that is involved in a task. For instance, if a person has struggled to learn a complex task (like assembling a rifle blindfolded) and rehearsed it many times it will become much more deeply ingrained in their memory than the steps involved in washing dishes. It is much easier to remember in detail a task that has required serious thought and effort than it is to remember the multitude of small details that fill in the average day that we don't think intently about.