second nature
noun [ U ] uk/ˌsek.ənd ˈneɪ.tʃər/ us/ˌsek.ənd ˈneɪ.tʃɚ/
第二天性；习性
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. 我曾经讨厌电脑，但现在使用电脑成为了我的习惯。