People use the term “nest egg” to refer to their life savings, their retirement savings, what they will live on after they stop working. “Nest egg” can also refer to any long-terms savings that are accumulated over time for a specific purpose. I wonder how many people know the origin of the phrase.
Among people that raise chickens, especially those in the egg business, it has long been known that leaving an egg in the nest will encourage hens to lay more. Maybe even get a hen started if she hasn’t laid yet. The practice of leaving an egg in the nest gives us “nest egg” — the nest egg is the egg that’s left in the nest. Nest eggs don’t necessarily have to be real eggs. Wooden or ceramic eggs seem to work just as well. The principle is the same: the egg farmer doesn’t eat or get rid of the nest egg. The nest egg is quite similar to “seed corn”, the seed that is saved from one year’s harvest for the next year’s planting, rather than being sold or otherwise used. (Maybe there’s some reason we don’t refer to our live savings as our “seed corn”, but I don’t know what it is.)
Thus, the next egg is something akin to what economists call “capital”: money or some other asset that is used to make money. Eat your nest egg, and you’ll have fewer eggs. Eat of your seed corn and there’s no crop next year. Spend your retirement savings, and it won’t be there to provide for you when you need it.