If something is second nature to you, you are so familiar with it that you can do it easily without needing to think very much about it: I used to hate computers, but using them is second nature to me now.

What does it mean if something is second nature?

: an acquired deeply ingrained habit or skill after a while, using the gearshift becomes second nature.

Why do we say 2nd nature?

This expression is a shortened form of an ancient proverb, Custom (or usage) is a second nature, first recorded in 1390. It alludes to the fact that very frequently repeating something makes it seem completely natural or inborn.