If the knocking at the door is twice, it is not opportunity, it is postman.

If the knocking at the door is loud and long, it is not opportunity, it is your relatives.

The postman always rings twice

Some people are in the habit of complaining about everything; even about the noise made by opportunity that knocks on the door.

He is miserable once who feels it, but twice who fears it before it comes.

The doctor asks the patient what is wrong, and then the patient asks the doctor what is wrong.