信心不足的英文：
to lack confidence

参考例句：

He was a little diffident,but quite self - possessed.
他有点信心不足，但很镇静。

And with these students he feels frustrated, inadequate, and even angry.
而且跟这些学生在一起时，他觉得灰心丧气，信心不足，甚至觉得气愤。

lack是什么意思：
n. 缺乏，不足
v. 缺乏，不足，没有

They lacked for nothing.
他们什么都不缺少。

lacking in impressiveness.
缺少令人难忘的特点。

People do not lack strength; they lack will
人们不缺力量,缺的是决心

The lack of rain aggravated the already serious lack of food.
缺少雨水加重了业已严重的食物缺乏。

It is a lack that should be remedied.
这是疏忽，得补救。

confidence是什么意思：
n. 自信；信任；知心人；秘密；大胆

Confidence is transferrable.
自信是可以转换的。

Have confidence in yourself.
得对自己有信心。

They have confidence in me.
他们对我有信心。

This is a further hit to business confidence and to household confidence.
这对企业界和一般家庭的信心而言，是一项打击。

He felt confident in the future.
他对未来充满信心。