A very simple task or project that requires very little mental or physical effort is often described as either a "piece of cake" or "easy as pie." The two idioms are very similar in nature, and are often used interchangeably when referring to an exceptionally easy job assignment. However, as any cook can attest, the actual creation of a pie can be a very complicated process for the baker. The "easy" in the expression may actually refer to the ease of eating the finished product. Some etymologists suggest the implied meaning behind the idiom is closer to "(as) easy as eating pie." This may refer to leading such a leisurely life that eating pies or other desserts are considered to be the only real challenge of the day.
The expression is often used to describe a work assignment so simple and effortless it should be easy to complete. The term could be used to refer to finding a particular location in an unfamiliar city with the help of a GPS navigation system, spotting the assigned target during a military bombing run with the proper coordinates, or even figuring out the killer's identity on a crime show once all the clues have been revealed. There are any number of situations which can be described as easy as pie once all the facts are in or clear instructions are provided.
There is no clear answer concerning the origin of this phrase, although the word "pie" has had several slang meanings over the years. During the 19th century, pie represented living the easy or simple life, similar to the modern use of "sunshine and lollipops" or other pie-in-the-sky analogies. A person could be described as "nice as pie" or "polite as pie" in popular novels such as Mark Twain's Huckleberry Finn. The act of eating pie was also used as a simile for other relatively easy accomplishments in sports or business.
This reference to simplicity and ease could also explain the use of the word "pie" in other expressions, such as pie-eyed and pie-in-the-sky. An especially unmotivated person might be judged so lazy that "he wouldn't take a job tasting pies in a pie factory." Whether it's a piece of cake or easy as pie, there is usually no doubt that the task at hand should be remarkably easy to accomplish.