I want to be the best, simple and plain.

我想成为最好的，就这么简单。

He is used to this kind of simple and plain life.

他已经习惯了这种粗朴的生活。

Like a picture, no frame, see it's simple and plain.

像一幅画，没有边框，它朴实无华。

I want to say the simple and plain truth that I love you.

我想说简单和纯粹的事实是我爱你。

The most profound thoughts are always those which are simple and plain.

最深刻的道理，往往是最简单和最朴素的。