I first recognized this trait in myself.这句话为什么用in?in oneself是固定用法吗?

问题描述:

I first recognized this trait in myself.这句话为什么用in?in oneself是固定用法吗?
还有believe myself 和believe in myself有啥区别呢?

in oneself是固定用法,“自身,本质上”;
一般不用believe myself believe sb.相信某人说的话
believe in myself 相信自己;信任自己