(idiomatic) Used to emphasize that two subjects are so different that they cannot coexist or agree with each other.

Having overconfidence in one's opinions that is impervious to failure.

Alternative form of misfortunes never come singly

Housework, which is generally considered women's work, is never finished.

It is unwise to seek personal acquaintance with people whom one has regarded with high esteem, as they often fail to fulfill one's expectations, resulting in disappointment.

Alternative form of barking dogs seldom bite

(Ireland) Those who fail to speak up fail to get what they want.

Alternative form of don't look a gift horse in the mouth

It is possible to learn new things, at any age; follow your desires and dreams.

(informal) Used to draw attention to a possible double entendre in the immediately preceding utterance of another speaker.