Piece of cake
Meaning: Something very easy to do
Originated in: 🇺🇸 United States of America
Earliest attestation: The Primrose Path by Ogden Nash (1936)
This idiom is an exaggerated expression of how easy something is. It is often used to reassure someone that a task will not be a challenge and can be completed with little effort. It can be used both for tasks that are genuinely simple and for complex tasks that are expected to be comparatively easy.
It is presumably derived from the idea that eating a piece of cake is a simple and enjoyable task. This would likely make it derivative of the similar simile “easy as pie”. Both phrases draw on the universally pleasant and straightforward experience of enjoying a dessert. Essentially everyone loves desserts like cakes and pies, so they became very representative of ease and pleasure.
It also resonates on a sensory level. Cake is literally an extremely soft and fluffy food. It requires no effort to eat and it seems naturally opposed to being “hard”. The fluffiness adds to the sensation of lightness and ease, suggesting that the task is almost weightless in its accomplishment.
The phrase is still in common use today, and it is often used in a casual or informal context. It is a friendly and reassuring way to tell someone that one can handle a task with ease.