我真笨，刚才为什么没想到这么做。

Wǒ zhēn bèn, gāngcái wèishénme méi xiǎngdào zhème zuò.

I'm really foolish, why didn't I think to do it that way just now?

我很笨。

Wǒ hěn bèn.

I'm stupid.

我虽然笨，但是我很勤奋。

Wǒ suīrán bèn, dànshì wǒ hěn qínfèn.

Although I'm dumb, I'm very hard working.