妄自菲薄的英文：
[Literal Meaning]
groundless/oneself/belittle
to unduly humble oneself

[解释]
过分看清自己。

[Explanation]
to undervalue oneself

[例子]
你也别妄自菲薄，相信自己靠实力是可以在竞赛中取得好成绩的。

[Example]
You should not undervalue yourself but believe that you won in the contest for your own excellence.

[英文等价词]
improperly belittle oneself; underestimate oen's own capabilities

Don't belittle yourself unduly
不要妄自菲薄。

have an inferiority complex;demean oneself;belittle;Underestimate one's achievements
妄自菲薄

There is always someone worse off than you. —— Aesop
总有人不如你。(不宜妄自菲薄)——伊索

Hide not your light under a bushel.
不要把灯藏在斗底下(切莫妄自菲薄)。

We must be realistic in our self-estimation, neither being conceited nor belittling ourselves.
我们对自己的估计应该实事求是，不要自高自大，也不要妄自菲薄。

But if someone as inconsequential as himself was worth of patronage, then obviously he shouldn't underestimate himself
可是自己是一个无足轻重的人，居然有被他收罗的资格，足见未可妄自菲薄。