What is the origin of the idiom "second nature" and when to use it?

The idiom "second nature" has its origins in the idea of acquired habits or skills becoming so ingrained and automatic that they seem as natural as one's primary, or "first," nature. It reflects the concept that repeated actions or behaviors can become almost instinctual, like a reflex. This phrase is often used to describe activities or abilities that individuals have practiced to the point where they require little conscious thought or effort.