Having the ability to solve problems by oneself reflects that the person is independent and has already grown up.

具有独立解决问题的能力，反映出一个人已经独立，已经长大了。

One is firmly established by oneself.

卓然自立。

One cannot live by oneself.

人不能单独生活。

One cannot play tennis by oneself.

一个人不能独自打网球。

I am to feel everything is by oneself.

我是觉得一切是由自己。