英語のことわざ

Opportunity seldom knocks twice

This is another proverb that encourages action. If you have the opportunity to do something that you want to do, you should do it — now. Otherwise you will not get a chance to do it again. It is very rare that you get a second chance. "Seldom" means "not often." The "knock" is a little more difficult to explain. Imagine "opportunity" as a person. He comes to your house and he "knocks" on your door. If you tell him that you're not interested, he will probably not come back, he will probably not knock on your door again.